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 $67.96   8.417%   $73.6802   $73.68   $73.70   $73.70  
  Purchase #2 $164.66   10.303%   $181.6249   $181.62   $181.60   $181.60  
  Purchase #3 $233.85   13.413%   $265.2163   $265.22   $265.20   $265.20  
  Purchase #4 $167.79   7.731%   $180.7618   $180.76   $180.75   $180.80  
  Purchase #5 $64.25   5.568%   $67.8274   $67.83   $67.85   $67.80  
  Purchase #6 $23.57   10.386%   $26.018   $26.02   $26.00   $26.00  
  Purchase #7 $163.27   5.791%   $172.725   $172.73   $172.75   $172.70  
  7 purchase totals = $885.35       $967.8536   $967.86   $967.85   $967.80