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 $66.25   3.123%   $68.319   $68.32   $68.30   $68.30  
  Purchase #2 $66.90   4.644%   $70.0068   $70.01   $70.00   $70.00  
  Purchase #3 $185.46   11.386%   $206.5765   $206.58   $206.60   $206.60  
  Purchase #4 $200.84   5.314%   $211.5126   $211.51   $211.50   $211.50  
  Purchase #5 $219.93   11.847%   $245.9851   $245.99   $246.00   $246.00  
  Purchase #6 $239.84   6.459%   $255.3313   $255.33   $255.35   $255.30  
  Purchase #7 $126.49   11.844%   $141.4715   $141.47   $141.45   $141.50  
  7 purchase totals = $1,105.71       $1,199.2028   $1,199.21   $1,199.20   $1,199.20