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 $174.73   11.277%   $194.4343   $194.43   $194.45   $194.40  
  Purchase #2 $41.78   10.534%   $46.1811   $46.18   $46.20   $46.20  
  Purchase #3 $184.39   4.282%   $192.2856   $192.29   $192.30   $192.30  
  Purchase #4 $154.38   7.596%   $166.1067   $166.11   $166.10   $166.10  
  Purchase #5 $207.67   13.736%   $236.1956   $236.20   $236.20   $236.20  
  Purchase #6 $10.51   6.301%   $11.1722   $11.17   $11.15   $11.20  
  Purchase #7 $165.42   11.400%   $184.2779   $184.28   $184.30   $184.30  
  7 purchase totals = $938.88       $1,030.6534   $1,030.66   $1,030.70   $1,030.70