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 $235.60   7.327%   $252.8624   $252.86   $252.85   $252.90  
  Purchase #2 $82.67   11.229%   $91.953   $91.95   $91.95   $92.00  
  Purchase #3 $37.54   11.174%   $41.7347   $41.73   $41.75   $41.70  
  Purchase #4 $23.57   10.199%   $25.9739   $25.97   $25.95   $26.00  
  Purchase #5 $75.88   10.797%   $84.0728   $84.07   $84.05   $84.10  
  Purchase #6 $218.70   11.499%   $243.8483   $243.85   $243.85   $243.80  
  Purchase #7 $159.83   10.198%   $176.1295   $176.13   $176.15   $176.10  
  7 purchase totals = $833.79       $916.5746   $916.56   $916.55   $916.60