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 $166.47   10.521%   $183.9843   $183.98   $184.00   $184.00  
  Purchase #2 $113.79   4.240%   $118.6147   $118.61   $118.60   $118.60  
  Purchase #3 $246.35   12.544%   $277.2521   $277.25   $277.25   $277.30  
  Purchase #4 $127.59   8.462%   $138.3867   $138.39   $138.40   $138.40  
  Purchase #5 $141.81   8.390%   $153.7079   $153.71   $153.70   $153.70  
  Purchase #6 $191.69   11.376%   $213.4967   $213.50   $213.50   $213.50  
  Purchase #7 $105.73   10.419%   $116.746   $116.75   $116.75   $116.70  
  7 purchase totals = $1,093.43       $1,202.1884   $1,202.19   $1,202.20   $1,202.20