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 $41.43   7.233%   $44.4266   $44.43   $44.45   $44.40  
  Purchase #2 $152.73   12.157%   $171.2974   $171.30   $171.30   $171.30  
  Purchase #3 $216.62   12.839%   $244.4318   $244.43   $244.45   $244.40  
  Purchase #4 $226.94   12.195%   $254.6153   $254.62   $254.60   $254.60  
  Purchase #5 $149.33   13.707%   $169.7987   $169.80   $169.80   $169.80  
  Purchase #6 $38.94   13.786%   $44.3083   $44.31   $44.30   $44.30  
  Purchase #7 $121.68   3.569%   $126.0228   $126.02   $126.00   $126.00  
  7 purchase totals = $947.67       $1,054.9009   $1,054.91   $1,054.90   $1,054.80