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 $122.60   10.540%   $135.522   $135.52   $135.50   $135.50  
  Purchase #2 $91.39   9.188%   $99.7869   $99.79   $99.80   $99.80  
  Purchase #3 $128.35   4.141%   $133.665   $133.67   $133.65   $133.70  
  Purchase #4 $135.50   5.332%   $142.7249   $142.72   $142.70   $142.70  
  Purchase #5 $246.96   5.355%   $260.1847   $260.18   $260.20   $260.20  
  Purchase #6 $37.45   6.336%   $39.8228   $39.82   $39.80   $39.80  
  Purchase #7 $94.43   5.349%   $99.4811   $99.48   $99.50   $99.50  
  7 purchase totals = $856.68       $911.1874   $911.18   $911.15   $911.20