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 $83.38   4.314%   $86.977   $86.98   $87.00   $87.00  
  Purchase #2 $119.33   5.747%   $126.1879   $126.19   $126.20   $126.20  
  Purchase #3 $240.80   4.478%   $251.583   $251.58   $251.60   $251.60  
  Purchase #4 $32.59   5.115%   $34.257   $34.26   $34.25   $34.30  
  Purchase #5 $40.27   10.190%   $44.3735   $44.37   $44.35   $44.40  
  Purchase #6 $59.57   10.765%   $65.9827   $65.98   $66.00   $66.00  
  Purchase #7 $213.63   6.856%   $228.2765   $228.28   $228.30   $228.30  
  7 purchase totals = $789.57       $837.6376   $837.64   $837.70   $837.80