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 $114.34   4.410%   $119.3824   $119.38   $119.40   $119.40  
  Purchase #2 $62.53   9.108%   $68.2252   $68.23   $68.25   $68.20  
  Purchase #3 $162.36   11.657%   $181.2863   $181.29   $181.30   $181.30  
  Purchase #4 $225.39   8.645%   $244.875   $244.88   $244.90   $244.90  
  Purchase #5 $178.43   13.642%   $202.7714   $202.77   $202.75   $202.80  
  Purchase #6 $246.29   9.250%   $269.0718   $269.07   $269.05   $269.10  
  Purchase #7 $23.92   13.767%   $27.2131   $27.21   $27.20   $27.20  
  7 purchase totals = $1,013.26       $1,112.8252   $1,112.83   $1,112.85   $1,112.90