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 $84.94   13.578%   $96.4732   $96.47   $96.45   $96.50  
  Purchase #2 $191.59   4.342%   $199.9088   $199.91   $199.90   $199.90  
  Purchase #3 $225.64   12.825%   $254.5783   $254.58   $254.60   $254.60  
  Purchase #4 $13.82   12.237%   $15.5112   $15.51   $15.50   $15.50  
  Purchase #5 $200.56   12.193%   $225.0143   $225.01   $225.00   $225.00  
  Purchase #6 $98.99   3.382%   $102.3378   $102.34   $102.35   $102.30  
  Purchase #7 $198.43   3.237%   $204.8532   $204.85   $204.85   $204.90  
  7 purchase totals = $1,013.97       $1,098.6768   $1,098.67   $1,098.65   $1,098.70