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 $146.94   6.343%   $156.2604   $156.26   $156.25   $156.30  
  Purchase #2 $97.46   13.864%   $110.9719   $110.97   $110.95   $111.00  
  Purchase #3 $106.84   7.734%   $115.103   $115.10   $115.10   $115.10  
  Purchase #4 $197.40   3.283%   $203.8806   $203.88   $203.90   $203.90  
  Purchase #5 $46.80   10.359%   $51.648   $51.65   $51.65   $51.60  
  Purchase #6 $106.81   9.383%   $116.832   $116.83   $116.85   $116.80  
  Purchase #7 $84.86   13.375%   $96.21   $96.21   $96.20   $96.20  
  7 purchase totals = $787.11       $850.9059   $850.90   $850.90   $850.90