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 $240.62   7.624%   $258.9649   $258.96   $258.95   $259.00  
  Purchase #2 $39.95   6.507%   $42.5495   $42.55   $42.55   $42.50  
  Purchase #3 $165.49   7.163%   $177.344   $177.34   $177.35   $177.30  
  Purchase #4 $219.92   5.482%   $231.976   $231.98   $232.00   $232.00  
  Purchase #5 $54.53   6.317%   $57.9747   $57.97   $57.95   $58.00  
  Purchase #6 $47.90   9.461%   $52.4318   $52.43   $52.45   $52.40  
  Purchase #7 $125.41   3.386%   $129.6564   $129.66   $129.65   $129.70  
  7 purchase totals = $893.82       $950.8973   $950.89   $950.90   $950.90