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 $153.96   5.872%   $163.0005   $163.00   $163.00   $163.00  
  Purchase #2 $87.75   5.628%   $92.6886   $92.69   $92.70   $92.70  
  Purchase #3 $154.88   6.303%   $164.6421   $164.64   $164.65   $164.60  
  Purchase #4 $92.82   10.294%   $102.3749   $102.37   $102.35   $102.40  
  Purchase #5 $152.96   11.757%   $170.9435   $170.94   $170.95   $170.90  
  Purchase #6 $92.57   5.456%   $97.6206   $97.62   $97.60   $97.60  
  Purchase #7 $206.50   13.104%   $233.5598   $233.56   $233.55   $233.60  
  7 purchase totals = $941.44       $1,024.8300   $1,024.82   $1,024.80   $1,024.80