Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $162.26   10.478%   $179.2616   $179.26   $179.25   $179.30  
  Purchase #2 $137.52   6.656%   $146.6733   $146.67   $146.65   $146.70  
  Purchase #3 $203.87   5.201%   $214.4733   $214.47   $214.45   $214.50  
  Purchase #4 $219.78   9.662%   $241.0151   $241.02   $241.00   $241.00  
  Purchase #5 $127.29   4.298%   $132.7609   $132.76   $132.75   $132.80  
  Purchase #6 $235.36   6.730%   $251.1997   $251.20   $251.20   $251.20  
  Purchase #7 $144.57   8.539%   $156.9148   $156.91   $156.90   $156.90  
  7 purchase totals = $1,230.65       $1,322.2987   $1,322.29   $1,322.20   $1,322.40