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 $77.98   12.804%   $87.9646   $87.96   $87.95   $88.00  
  Purchase #2 $162.49   9.247%   $177.5155   $177.52   $177.50   $177.50  
  Purchase #3 $74.27   11.715%   $82.9707   $82.97   $82.95   $83.00  
  Purchase #4 $125.97   9.227%   $137.5933   $137.59   $137.60   $137.60  
  Purchase #5 $218.53   5.850%   $231.314   $231.31   $231.30   $231.30  
  Purchase #6 $172.93   7.498%   $185.8963   $185.90   $185.90   $185.90  
  Purchase #7 $133.83   6.140%   $142.0472   $142.05   $142.05   $142.00  
  7 purchase totals = $966.00       $1,045.3016   $1,045.30   $1,045.25   $1,045.30