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 $132.77   13.507%   $150.7032   $150.70   $150.70   $150.70  
  Purchase #2 $58.94   13.123%   $66.6747   $66.67   $66.65   $66.70  
  Purchase #3 $22.75   12.465%   $25.5858   $25.59   $25.60   $25.60  
  Purchase #4 $239.42   9.838%   $262.9741   $262.97   $262.95   $263.00  
  Purchase #5 $48.46   9.379%   $53.0051   $53.01   $53.00   $53.00  
  Purchase #6 $34.41   5.169%   $36.1887   $36.19   $36.20   $36.20  
  Purchase #7 $117.96   3.336%   $121.8951   $121.90   $121.90   $121.90  
  7 purchase totals = $654.71       $717.0267   $717.03   $717.00   $717.10