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 $54.51   8.469%   $59.1265   $59.13   $59.15   $59.10  
  Purchase #2 $221.99   6.511%   $236.4438   $236.44   $236.45   $236.40  
  Purchase #3 $153.74   8.426%   $166.6941   $166.69   $166.70   $166.70  
  Purchase #4 $28.70   13.707%   $32.6339   $32.63   $32.65   $32.60  
  Purchase #5 $209.74   11.731%   $234.3446   $234.34   $234.35   $234.30  
  Purchase #6 $165.89   8.159%   $179.425   $179.43   $179.45   $179.40  
  Purchase #7 $186.69   6.639%   $199.0843   $199.08   $199.10   $199.10  
  7 purchase totals = $1,021.26       $1,107.7522   $1,107.74   $1,107.85   $1,107.60