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 $119.46   11.347%   $133.0151   $133.02   $133.00   $133.00  
  Purchase #2 $222.77   9.732%   $244.45   $244.45   $244.45   $244.50  
  Purchase #3 $246.59   10.795%   $273.2094   $273.21   $273.20   $273.20  
  Purchase #4 $122.64   12.655%   $138.1601   $138.16   $138.15   $138.20  
  Purchase #5 $163.45   6.774%   $174.5221   $174.52   $174.50   $174.50  
  Purchase #6 $211.86   4.383%   $221.1458   $221.15   $221.15   $221.10  
  Purchase #7 $127.29   11.444%   $141.8571   $141.86   $141.85   $141.90  
  7 purchase totals = $1,214.06       $1,326.3596   $1,326.37   $1,326.30   $1,326.40