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 $57.42   12.637%   $64.6762   $64.68   $64.70   $64.70  
  Purchase #2 $152.89   10.503%   $168.948   $168.95   $168.95   $168.90  
  Purchase #3 $131.96   13.257%   $149.4539   $149.45   $149.45   $149.50  
  Purchase #4 $223.36   9.641%   $244.8941   $244.89   $244.90   $244.90  
  Purchase #5 $34.50   6.363%   $36.6952   $36.70   $36.70   $36.70  
  Purchase #6 $217.84   7.629%   $234.459   $234.46   $234.45   $234.50  
  Purchase #7 $105.82   3.756%   $109.7946   $109.79   $109.80   $109.80  
  7 purchase totals = $923.79       $1,008.9210   $1,008.92   $1,008.95   $1,009.00