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 $62.83   12.401%   $70.6215   $70.62   $70.60   $70.60  
  Purchase #2 $69.77   12.667%   $78.6078   $78.61   $78.60   $78.60  
  Purchase #3 $154.94   12.486%   $174.2858   $174.29   $174.30   $174.30  
  Purchase #4 $25.49   6.202%   $27.0709   $27.07   $27.05   $27.10  
  Purchase #5 $138.64   8.206%   $150.0168   $150.02   $150.00   $150.00  
  Purchase #6 $192.37   6.260%   $204.4124   $204.41   $204.40   $204.40  
  Purchase #7 $81.27   13.641%   $92.356   $92.36   $92.35   $92.40  
  7 purchase totals = $725.31       $797.3712   $797.38   $797.30   $797.40