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 $64.61   13.143%   $73.1017   $73.10   $73.10   $73.10  
  Purchase #2 $91.82   11.483%   $102.3637   $102.36   $102.35   $102.40  
  Purchase #3 $56.39   3.191%   $58.1894   $58.19   $58.20   $58.20  
  Purchase #4 $218.54   9.758%   $239.8651   $239.87   $239.85   $239.90  
  Purchase #5 $106.48   3.681%   $110.3995   $110.40   $110.40   $110.40  
  Purchase #6 $224.91   9.632%   $246.5733   $246.57   $246.55   $246.60  
  Purchase #7 $204.92   6.561%   $218.3648   $218.36   $218.35   $218.40  
  7 purchase totals = $967.67       $1,048.8575   $1,048.85   $1,048.80   $1,049.00