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 $52.84   10.152%   $58.2043   $58.20   $58.20   $58.20  
  Purchase #2 $205.91   8.291%   $222.982   $222.98   $223.00   $223.00  
  Purchase #3 $168.70   9.372%   $184.5106   $184.51   $184.50   $184.50  
  Purchase #4 $237.70   8.164%   $257.1058   $257.11   $257.10   $257.10  
  Purchase #5 $84.65   11.247%   $94.1706   $94.17   $94.15   $94.20  
  Purchase #6 $195.54   5.723%   $206.7308   $206.73   $206.75   $206.70  
  Purchase #7 $10.32   4.334%   $10.7673   $10.77   $10.75   $10.80  
  7 purchase totals = $955.66       $1,034.4714   $1,034.47   $1,034.45   $1,034.50