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 $96.32   11.251%   $107.157   $107.16   $107.15   $107.20  
  Purchase #2 $61.95   7.755%   $66.7542   $66.75   $66.75   $66.80  
  Purchase #3 $107.65   5.616%   $113.6956   $113.70   $113.70   $113.70  
  Purchase #4 $194.28   3.556%   $201.1886   $201.19   $201.20   $201.20  
  Purchase #5 $236.80   7.214%   $253.8828   $253.88   $253.90   $253.90  
  Purchase #6 $73.31   7.854%   $79.0678   $79.07   $79.05   $79.10  
  Purchase #7 $93.83   10.514%   $103.6953   $103.70   $103.70   $103.70  
  7 purchase totals = $864.14       $925.4413   $925.45   $925.45   $925.60