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 $126.59   3.632%   $131.1877   $131.19   $131.20   $131.20  
  Purchase #2 $243.55   9.312%   $266.2294   $266.23   $266.25   $266.20  
  Purchase #3 $12.80   8.405%   $13.8758   $13.88   $13.90   $13.90  
  Purchase #4 $246.34   3.323%   $254.5259   $254.53   $254.55   $254.50  
  Purchase #5 $84.99   10.683%   $94.0695   $94.07   $94.05   $94.10  
  Purchase #6 $200.46   9.211%   $218.9244   $218.92   $218.90   $218.90  
  Purchase #7 $83.92   5.245%   $88.3216   $88.32   $88.30   $88.30  
  7 purchase totals = $998.65       $1,067.1343   $1,067.14   $1,067.15   $1,067.10