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 $244.64   12.651%   $275.5894   $275.59   $275.60   $275.60  
  Purchase #2 $95.79   9.782%   $105.1602   $105.16   $105.15   $105.20  
  Purchase #3 $204.69   13.438%   $232.1962   $232.20   $232.20   $232.20  
  Purchase #4 $59.94   6.865%   $64.0549   $64.05   $64.05   $64.10  
  Purchase #5 $112.65   13.162%   $127.477   $127.48   $127.50   $127.50  
  Purchase #6 $211.96   9.711%   $232.5434   $232.54   $232.55   $232.50  
  Purchase #7 $8.97   10.437%   $9.9062   $9.91   $9.90   $9.90  
  7 purchase totals = $938.64       $1,046.9273   $1,046.93   $1,046.95   $1,047.00