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 $158.39   6.673%   $168.9594   $168.96   $168.95   $169.00  
  Purchase #2 $35.55   8.666%   $38.6308   $38.63   $38.65   $38.60  
  Purchase #3 $15.33   7.843%   $16.5323   $16.53   $16.55   $16.50  
  Purchase #4 $160.87   12.257%   $180.5878   $180.59   $180.60   $180.60  
  Purchase #5 $42.69   7.612%   $45.9396   $45.94   $45.95   $45.90  
  Purchase #6 $117.49   5.787%   $124.2891   $124.29   $124.30   $124.30  
  Purchase #7 $159.29   9.874%   $175.0183   $175.02   $175.00   $175.00  
  7 purchase totals = $689.61       $749.9573   $749.96   $750.00   $749.90