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 $202.78   11.293%   $225.6799   $225.68   $225.70   $225.70  
  Purchase #2 $85.46   9.344%   $93.4454   $93.45   $93.45   $93.40  
  Purchase #3 $66.62   3.272%   $68.7998   $68.80   $68.80   $68.80  
  Purchase #4 $245.29   11.474%   $273.4346   $273.43   $273.45   $273.40  
  Purchase #5 $11.66   12.547%   $13.123   $13.12   $13.10   $13.10  
  Purchase #6 $180.86   11.211%   $201.1362   $201.14   $201.15   $201.10  
  Purchase #7 $183.77   6.289%   $195.3273   $195.33   $195.35   $195.30  
  7 purchase totals = $976.44       $1,070.9462   $1,070.95   $1,071.00   $1,070.80