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 $25.99   8.817%   $28.2815   $28.28   $28.30   $28.30  
  Purchase #2 $219.45   11.288%   $244.2215   $244.22   $244.20   $244.20  
  Purchase #3 $145.68   11.586%   $162.5585   $162.56   $162.55   $162.60  
  Purchase #4 $120.61   5.343%   $127.0542   $127.05   $127.05   $127.10  
  Purchase #5 $116.67   12.655%   $131.4346   $131.43   $131.45   $131.40  
  Purchase #6 $106.36   9.551%   $116.5184   $116.52   $116.50   $116.50  
  Purchase #7 $138.34   9.785%   $151.8766   $151.88   $151.90   $151.90  
  7 purchase totals = $873.10       $961.9453   $961.94   $961.95   $962.00