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 $67.30   10.873%   $74.6175   $74.62   $74.60   $74.60  
  Purchase #2 $180.50   4.334%   $188.3229   $188.32   $188.30   $188.30  
  Purchase #3 $190.26   6.211%   $202.077   $202.08   $202.10   $202.10  
  Purchase #4 $36.49   12.154%   $40.925   $40.93   $40.95   $40.90  
  Purchase #5 $199.84   10.287%   $220.3975   $220.40   $220.40   $220.40  
  Purchase #6 $77.59   9.429%   $84.906   $84.91   $84.90   $84.90  
  Purchase #7 $241.31   7.317%   $258.9667   $258.97   $258.95   $259.00  
  7 purchase totals = $993.29       $1,070.2126   $1,070.23   $1,070.20   $1,070.20