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 $89.81   5.314%   $94.5825   $94.58   $94.60   $94.60  
  Purchase #2 $236.96   4.488%   $247.5948   $247.59   $247.60   $247.60  
  Purchase #3 $87.70   5.825%   $92.8085   $92.81   $92.80   $92.80  
  Purchase #4 $134.52   3.452%   $139.1636   $139.16   $139.15   $139.20  
  Purchase #5 $155.71   7.253%   $167.0036   $167.00   $167.00   $167.00  
  Purchase #6 $176.45   13.250%   $199.8296   $199.83   $199.85   $199.80  
  Purchase #7 $57.94   11.731%   $64.7369   $64.74   $64.75   $64.70  
  7 purchase totals = $939.09       $1,005.7195   $1,005.71   $1,005.75   $1,005.70