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 $78.44   11.480%   $87.4449   $87.44   $87.45   $87.40  
  Purchase #2 $205.59   6.828%   $219.6277   $219.63   $219.65   $219.60  
  Purchase #3 $244.87   7.393%   $262.9732   $262.97   $262.95   $263.00  
  Purchase #4 $210.92   11.709%   $235.6166   $235.62   $235.60   $235.60  
  Purchase #5 $166.99   5.511%   $176.1928   $176.19   $176.20   $176.20  
  Purchase #6 $219.63   8.781%   $238.9157   $238.92   $238.90   $238.90  
  Purchase #7 $210.55   6.375%   $223.9726   $223.97   $223.95   $224.00  
  7 purchase totals = $1,336.99       $1,444.7435   $1,444.74   $1,444.70   $1,444.70