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 $59.94   12.325%   $67.3276   $67.33   $67.35   $67.30  
  Purchase #2 $198.96   12.308%   $223.448   $223.45   $223.45   $223.40  
  Purchase #3 $126.28   4.125%   $131.4891   $131.49   $131.50   $131.50  
  Purchase #4 $241.86   8.726%   $262.9647   $262.96   $262.95   $263.00  
  Purchase #5 $128.86   7.529%   $138.5619   $138.56   $138.55   $138.60  
  Purchase #6 $87.80   11.133%   $97.5748   $97.57   $97.55   $97.60  
  Purchase #7 $53.32   9.172%   $58.2105   $58.21   $58.20   $58.20  
  7 purchase totals = $897.02       $979.5766   $979.57   $979.55   $979.60