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 $48.62   10.657%   $53.8014   $53.80   $53.80   $53.80  
  Purchase #2 $146.35   11.393%   $163.0237   $163.02   $163.00   $163.00  
  Purchase #3 $29.66   7.263%   $31.8142   $31.81   $31.80   $31.80  
  Purchase #4 $35.91   6.412%   $38.2125   $38.21   $38.20   $38.20  
  Purchase #5 $157.65   7.332%   $169.2089   $169.21   $169.20   $169.20  
  Purchase #6 $50.57   5.614%   $53.409   $53.41   $53.40   $53.40  
  Purchase #7 $233.48   3.512%   $241.6798   $241.68   $241.70   $241.70  
  7 purchase totals = $702.24       $751.1495   $751.14   $751.10   $751.10