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 $59.75   8.515%   $64.8377   $64.84   $64.85   $64.80  
  Purchase #2 $34.58   6.124%   $36.6977   $36.70   $36.70   $36.70  
  Purchase #3 $32.44   7.828%   $34.9794   $34.98   $35.00   $35.00  
  Purchase #4 $143.32   4.292%   $149.4713   $149.47   $149.45   $149.50  
  Purchase #5 $235.91   13.185%   $267.0147   $267.01   $267.00   $267.00  
  Purchase #6 $244.36   12.793%   $275.621   $275.62   $275.60   $275.60  
  Purchase #7 $15.66   9.627%   $17.1676   $17.17   $17.15   $17.20  
  7 purchase totals = $766.02       $845.7894   $845.79   $845.75   $845.80