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 $46.99   3.132%   $48.4617   $48.46   $48.45   $48.50  
  Purchase #2 $243.88   7.610%   $262.4393   $262.44   $262.45   $262.40  
  Purchase #3 $88.45   9.280%   $96.6582   $96.66   $96.65   $96.70  
  Purchase #4 $167.57   8.134%   $181.2001   $181.20   $181.20   $181.20  
  Purchase #5 $114.47   10.844%   $126.8831   $126.88   $126.90   $126.90  
  Purchase #6 $157.73   8.435%   $171.0345   $171.03   $171.05   $171.00  
  Purchase #7 $106.87   9.469%   $116.9895   $116.99   $117.00   $117.00  
  7 purchase totals = $925.96       $1,003.6664   $1,003.66   $1,003.70   $1,003.70