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 $134.45   13.512%   $152.6169   $152.62   $152.60   $152.60  
  Purchase #2 $211.57   12.707%   $238.4542   $238.45   $238.45   $238.50  
  Purchase #3 $152.71   13.283%   $172.9945   $172.99   $173.00   $173.00  
  Purchase #4 $99.79   8.627%   $108.3989   $108.40   $108.40   $108.40  
  Purchase #5 $65.60   9.586%   $71.8884   $71.89   $71.90   $71.90  
  Purchase #6 $16.57   7.647%   $17.8371   $17.84   $17.85   $17.80  
  Purchase #7 $150.32   8.719%   $163.4264   $163.43   $163.45   $163.40  
  7 purchase totals = $831.01       $925.6164   $925.62   $925.65   $925.60