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 $119.94   3.263%   $123.8536   $123.85   $123.85   $123.90  
  Purchase #2 $14.45   12.164%   $16.2077   $16.21   $16.20   $16.20  
  Purchase #3 $157.36   12.543%   $177.0977   $177.10   $177.10   $177.10  
  Purchase #4 $71.97   13.864%   $81.9479   $81.95   $81.95   $81.90  
  Purchase #5 $236.77   8.547%   $257.0067   $257.01   $257.00   $257.00  
  Purchase #6 $75.31   13.448%   $85.4377   $85.44   $85.45   $85.40  
  Purchase #7 $68.61   10.395%   $75.742   $75.74   $75.75   $75.70  
  7 purchase totals = $744.41       $817.2933   $817.30   $817.30   $817.20