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 $94.29   3.776%   $97.8504   $97.85   $97.85   $97.90  
  Purchase #2 $204.58   11.685%   $228.4852   $228.49   $228.50   $228.50  
  Purchase #3 $52.56   7.140%   $56.3128   $56.31   $56.30   $56.30  
  Purchase #4 $107.71   5.541%   $113.6782   $113.68   $113.70   $113.70  
  Purchase #5 $100.78   6.471%   $107.3015   $107.30   $107.30   $107.30  
  Purchase #6 $171.85   7.636%   $184.9725   $184.97   $184.95   $185.00  
  Purchase #7 $156.39   3.670%   $162.1295   $162.13   $162.15   $162.10  
  7 purchase totals = $888.16       $950.7301   $950.73   $950.75   $950.80