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 $93.65   6.253%   $99.5059   $99.51   $99.50   $99.50  
  Purchase #2 $140.36   9.188%   $153.2563   $153.26   $153.25   $153.30  
  Purchase #3 $121.46   13.277%   $137.5862   $137.59   $137.60   $137.60  
  Purchase #4 $156.87   8.771%   $170.6291   $170.63   $170.65   $170.60  
  Purchase #5 $193.94   5.335%   $204.2867   $204.29   $204.30   $204.30  
  Purchase #6 $61.68   6.433%   $65.6479   $65.65   $65.65   $65.60  
  Purchase #7 $181.51   7.518%   $195.1559   $195.16   $195.15   $195.20  
  7 purchase totals = $949.47       $1,026.0680   $1,026.09   $1,026.10   $1,026.10