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 $84.92   10.742%   $94.0421   $94.04   $94.05   $94.00  
  Purchase #2 $37.88   12.725%   $42.7002   $42.70   $42.70   $42.70  
  Purchase #3 $107.88   12.318%   $121.1687   $121.17   $121.15   $121.20  
  Purchase #4 $41.77   13.301%   $47.3258   $47.33   $47.35   $47.30  
  Purchase #5 $202.67   13.483%   $229.996   $230.00   $230.00   $230.00  
  Purchase #6 $149.50   12.718%   $168.5134   $168.51   $168.50   $168.50  
  Purchase #7 $66.79   12.183%   $74.927   $74.93   $74.95   $74.90  
  7 purchase totals = $691.41       $778.6732   $778.68   $778.70   $778.60