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 $61.98   13.764%   $70.5109   $70.51   $70.50   $70.50  
  Purchase #2 $182.57   9.217%   $199.3975   $199.40   $199.40   $199.40  
  Purchase #3 $70.94   13.182%   $80.2913   $80.29   $80.30   $80.30  
  Purchase #4 $221.53   11.384%   $246.749   $246.75   $246.75   $246.70  
  Purchase #5 $47.25   3.733%   $49.0138   $49.01   $49.00   $49.00  
  Purchase #6 $65.53   13.402%   $74.3123   $74.31   $74.30   $74.30  
  Purchase #7 $196.44   5.271%   $206.7944   $206.79   $206.80   $206.80  
  7 purchase totals = $846.24       $927.0692   $927.06   $927.05   $927.00