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 $193.55   6.380%   $205.8985   $205.90   $205.90   $205.90  
  Purchase #2 $62.93   7.771%   $67.8203   $67.82   $67.80   $67.80  
  Purchase #3 $217.31   7.432%   $233.4605   $233.46   $233.45   $233.50  
  Purchase #4 $165.29   4.854%   $173.3132   $173.31   $173.30   $173.30  
  Purchase #5 $244.80   5.703%   $258.7609   $258.76   $258.75   $258.80  
  Purchase #6 $26.99   7.275%   $28.9535   $28.95   $28.95   $29.00  
  Purchase #7 $179.98   6.267%   $191.2593   $191.26   $191.25   $191.30  
  7 purchase totals = $1,090.85       $1,159.4662   $1,159.46   $1,159.40   $1,159.60