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 $32.89   12.674%   $37.0585   $37.06   $37.05   $37.10  
  Purchase #2 $197.84   6.650%   $210.9964   $211.00   $211.00   $211.00  
  Purchase #3 $125.50   10.508%   $138.6875   $138.69   $138.70   $138.70  
  Purchase #4 $221.77   9.553%   $242.9557   $242.96   $242.95   $243.00  
  Purchase #5 $231.95   4.782%   $243.0418   $243.04   $243.05   $243.00  
  Purchase #6 $73.47   3.342%   $75.9254   $75.93   $75.95   $75.90  
  Purchase #7 $71.62   9.771%   $78.618   $78.62   $78.60   $78.60  
  7 purchase totals = $955.04       $1,027.2833   $1,027.30   $1,027.30   $1,027.30