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 $62.38   8.485%   $67.6729   $67.67   $67.65   $67.70  
  Purchase #2 $93.57   8.209%   $101.2512   $101.25   $101.25   $101.30  
  Purchase #3 $195.67   8.861%   $213.0083   $213.01   $213.00   $213.00  
  Purchase #4 $150.31   8.818%   $163.5643   $163.56   $163.55   $163.60  
  Purchase #5 $194.60   8.224%   $210.6039   $210.60   $210.60   $210.60  
  Purchase #6 $36.47   8.345%   $39.5134   $39.51   $39.50   $39.50  
  Purchase #7 $81.25   11.769%   $90.8123   $90.81   $90.80   $90.80  
  7 purchase totals = $814.25       $886.4263   $886.41   $886.35   $886.50