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 $93.49   6.313%   $99.392   $99.39   $99.40   $99.40  
  Purchase #2 $184.31   9.599%   $202.0019   $202.00   $202.00   $202.00  
  Purchase #3 $147.43   3.604%   $152.7434   $152.74   $152.75   $152.70  
  Purchase #4 $200.70   10.678%   $222.1307   $222.13   $222.15   $222.10  
  Purchase #5 $108.31   4.138%   $112.7919   $112.79   $112.80   $112.80  
  Purchase #6 $87.35   7.783%   $94.1485   $94.15   $94.15   $94.10  
  Purchase #7 $180.86   13.549%   $205.3647   $205.36   $205.35   $205.40  
  7 purchase totals = $1,002.45       $1,088.5731   $1,088.56   $1,088.60   $1,088.50