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 $58.70   6.165%   $62.3189   $62.32   $62.30   $62.30  
  Purchase #2 $230.79   11.609%   $257.5824   $257.58   $257.60   $257.60  
  Purchase #3 $109.52   12.168%   $122.8464   $122.85   $122.85   $122.80  
  Purchase #4 $5.50   4.487%   $5.7468   $5.75   $5.75   $5.70  
  Purchase #5 $175.25   4.402%   $182.9645   $182.96   $182.95   $183.00  
  Purchase #6 $8.84   4.808%   $9.265   $9.27   $9.25   $9.30  
  Purchase #7 $250.75   12.287%   $281.5597   $281.56   $281.55   $281.60  
  7 purchase totals = $839.35       $922.2837   $922.29   $922.25   $922.30