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 $88.77   9.873%   $97.5343   $97.53   $97.55   $97.50  
  Purchase #2 $211.83   5.253%   $222.9574   $222.96   $222.95   $223.00  
  Purchase #3 $71.67   4.501%   $74.8959   $74.90   $74.90   $74.90  
  Purchase #4 $188.43   7.721%   $202.9787   $202.98   $203.00   $203.00  
  Purchase #5 $173.71   11.757%   $194.1331   $194.13   $194.15   $194.10  
  Purchase #6 $247.97   5.197%   $260.857   $260.86   $260.85   $260.90  
  Purchase #7 $84.89   3.544%   $87.8985   $87.90   $87.90   $87.90  
  7 purchase totals = $1,067.27       $1,141.2549   $1,141.26   $1,141.30   $1,141.30