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 $73.27   5.524%   $77.3174   $77.32   $77.30   $77.30  
  Purchase #2 $204.56   10.470%   $225.9774   $225.98   $226.00   $226.00  
  Purchase #3 $58.56   13.264%   $66.3274   $66.33   $66.35   $66.30  
  Purchase #4 $234.77   4.230%   $244.7008   $244.70   $244.70   $244.70  
  Purchase #5 $236.83   5.701%   $250.3317   $250.33   $250.35   $250.30  
  Purchase #6 $234.92   3.385%   $242.872   $242.87   $242.85   $242.90  
  Purchase #7 $105.89   12.781%   $119.4238   $119.42   $119.40   $119.40  
  7 purchase totals = $1,148.80       $1,226.9505   $1,226.95   $1,226.95   $1,226.90