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 $38.27   13.103%   $43.2845   $43.28   $43.30   $43.30  
  Purchase #2 $216.92   8.628%   $235.6359   $235.64   $235.65   $235.60  
  Purchase #3 $187.30   7.514%   $201.3737   $201.37   $201.35   $201.40  
  Purchase #4 $45.62   4.611%   $47.7235   $47.72   $47.70   $47.70  
  Purchase #5 $90.59   12.772%   $102.1602   $102.16   $102.15   $102.20  
  Purchase #6 $183.75   4.162%   $191.3977   $191.40   $191.40   $191.40  
  Purchase #7 $64.48   11.266%   $71.7443   $71.74   $71.75   $71.70  
  7 purchase totals = $826.93       $893.3198   $893.31   $893.30   $893.30