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 $171.53   11.517%   $191.2851   $191.29   $191.30   $191.30  
  Purchase #2 $178.93   4.288%   $186.6025   $186.60   $186.60   $186.60  
  Purchase #3 $94.26   5.110%   $99.0767   $99.08   $99.10   $99.10  
  Purchase #4 $201.56   11.561%   $224.8624   $224.86   $224.85   $224.90  
  Purchase #5 $22.56   5.115%   $23.7139   $23.71   $23.70   $23.70  
  Purchase #6 $91.37   3.604%   $94.663   $94.66   $94.65   $94.70  
  Purchase #7 $133.80   9.650%   $146.7117   $146.71   $146.70   $146.70  
  7 purchase totals = $894.01       $966.9153   $966.91   $966.90   $967.00