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 $236.80   13.109%   $267.8421   $267.84   $267.85   $267.80  
  Purchase #2 $116.60   3.406%   $120.5714   $120.57   $120.55   $120.60  
  Purchase #3 $127.47   4.566%   $133.2903   $133.29   $133.30   $133.30  
  Purchase #4 $166.51   11.137%   $185.0542   $185.05   $185.05   $185.10  
  Purchase #5 $149.62   13.753%   $170.1972   $170.20   $170.20   $170.20  
  Purchase #6 $235.28   13.626%   $267.3393   $267.34   $267.35   $267.30  
  Purchase #7 $91.55   9.243%   $100.012   $100.01   $100.00   $100.00  
  7 purchase totals = $1,123.83       $1,244.3065   $1,244.30   $1,244.30   $1,244.30