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 $182.77   11.337%   $203.4906   $203.49   $203.50   $203.50  
  Purchase #2 $95.98   9.132%   $104.7449   $104.74   $104.75   $104.70  
  Purchase #3 $170.49   8.603%   $185.1573   $185.16   $185.15   $185.20  
  Purchase #4 $109.75   9.301%   $119.9578   $119.96   $119.95   $120.00  
  Purchase #5 $48.79   10.300%   $53.8154   $53.82   $53.80   $53.80  
  Purchase #6 $83.46   5.375%   $87.946   $87.95   $87.95   $87.90  
  Purchase #7 $227.83   11.254%   $253.47   $253.47   $253.45   $253.50  
  7 purchase totals = $919.07       $1,008.5820   $1,008.59   $1,008.55   $1,008.60