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 $233.64   12.608%   $263.0973   $263.10   $263.10   $263.10  
  Purchase #2 $218.35   11.691%   $243.8773   $243.88   $243.90   $243.90  
  Purchase #3 $73.63   10.140%   $81.0961   $81.10   $81.10   $81.10  
  Purchase #4 $208.71   9.422%   $228.3747   $228.37   $228.35   $228.40  
  Purchase #5 $119.35   11.224%   $132.7458   $132.75   $132.75   $132.70  
  Purchase #6 $89.78   3.498%   $92.9205   $92.92   $92.90   $92.90  
  Purchase #7 $11.40   12.599%   $12.8363   $12.84   $12.85   $12.80  
  7 purchase totals = $954.86       $1,054.9480   $1,054.96   $1,054.95   $1,054.90