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 $224.91   11.578%   $250.9501   $250.95   $250.95   $251.00  
  Purchase #2 $67.47   6.628%   $71.9419   $71.94   $71.95   $71.90  
  Purchase #3 $161.81   12.136%   $181.4473   $181.45   $181.45   $181.40  
  Purchase #4 $202.33   3.646%   $209.707   $209.71   $209.70   $209.70  
  Purchase #5 $120.45   8.646%   $130.8641   $130.86   $130.85   $130.90  
  Purchase #6 $13.89   5.697%   $14.6813   $14.68   $14.70   $14.70  
  Purchase #7 $156.43   11.507%   $174.4304   $174.43   $174.45   $174.40  
  7 purchase totals = $947.29       $1,034.0221   $1,034.02   $1,034.05   $1,034.00