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 $178.96   13.263%   $202.6955   $202.70   $202.70   $202.70  
  Purchase #2 $103.50   3.335%   $106.9517   $106.95   $106.95   $107.00  
  Purchase #3 $220.32   11.629%   $245.941   $245.94   $245.95   $245.90  
  Purchase #4 $83.85   6.731%   $89.4939   $89.49   $89.50   $89.50  
  Purchase #5 $132.74   5.586%   $140.1549   $140.15   $140.15   $140.20  
  Purchase #6 $161.29   7.424%   $173.2642   $173.26   $173.25   $173.30  
  Purchase #7 $59.98   5.560%   $63.3149   $63.31   $63.30   $63.30  
  7 purchase totals = $940.64       $1,021.8161   $1,021.80   $1,021.80   $1,021.90