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 $97.41   4.737%   $102.0243   $102.02   $102.00   $102.00  
  Purchase #2 $238.43   9.581%   $261.274   $261.27   $261.25   $261.30  
  Purchase #3 $61.33   5.751%   $64.8571   $64.86   $64.85   $64.90  
  Purchase #4 $194.83   3.417%   $201.4873   $201.49   $201.50   $201.50  
  Purchase #5 $157.44   11.663%   $175.8022   $175.80   $175.80   $175.80  
  Purchase #6 $116.31   6.192%   $123.5119   $123.51   $123.50   $123.50  
  Purchase #7 $23.69   6.867%   $25.3168   $25.32   $25.30   $25.30  
  7 purchase totals = $889.44       $954.2736   $954.27   $954.20   $954.30