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 $197.83   13.399%   $224.3372   $224.34   $224.35   $224.30  
  Purchase #2 $176.60   13.631%   $200.6723   $200.67   $200.65   $200.70  
  Purchase #3 $181.44   13.290%   $205.5534   $205.55   $205.55   $205.60  
  Purchase #4 $108.32   7.516%   $116.4613   $116.46   $116.45   $116.50  
  Purchase #5 $142.87   11.873%   $159.833   $159.83   $159.85   $159.80  
  Purchase #6 $210.57   7.285%   $225.91   $225.91   $225.90   $225.90  
  Purchase #7 $60.28   9.657%   $66.1012   $66.10   $66.10   $66.10  
  7 purchase totals = $1,077.91       $1,198.8684   $1,198.86   $1,198.85   $1,198.90