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 $36.49   12.404%   $41.0162   $41.02   $41.00   $41.00  
  Purchase #2 $123.70   11.580%   $138.0245   $138.02   $138.00   $138.00  
  Purchase #3 $56.47   12.346%   $63.4418   $63.44   $63.45   $63.40  
  Purchase #4 $125.81   5.598%   $132.8528   $132.85   $132.85   $132.90  
  Purchase #5 $43.79   5.580%   $46.2335   $46.23   $46.25   $46.20  
  Purchase #6 $241.52   13.712%   $274.6372   $274.64   $274.65   $274.60  
  Purchase #7 $208.25   10.759%   $230.6556   $230.66   $230.65   $230.70  
  7 purchase totals = $836.03       $926.8616   $926.86   $926.85   $926.80