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 $31.37   8.240%   $33.9549   $33.95   $33.95   $34.00  
  Purchase #2 $233.59   9.353%   $255.4377   $255.44   $255.45   $255.40  
  Purchase #3 $231.47   11.219%   $257.4386   $257.44   $257.45   $257.40  
  Purchase #4 $170.94   9.748%   $187.6032   $187.60   $187.60   $187.60  
  Purchase #5 $101.69   9.809%   $111.6648   $111.66   $111.65   $111.70  
  Purchase #6 $205.99   8.268%   $223.0213   $223.02   $223.00   $223.00  
  Purchase #7 $207.76   11.773%   $232.2196   $232.22   $232.20   $232.20  
  7 purchase totals = $1,182.81       $1,301.3401   $1,301.33   $1,301.30   $1,301.30