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 $62.48   9.471%   $68.3975   $68.40   $68.40   $68.40  
  Purchase #2 $211.71   10.407%   $233.7427   $233.74   $233.75   $233.70  
  Purchase #3 $80.64   6.378%   $85.7832   $85.78   $85.80   $85.80  
  Purchase #4 $185.45   8.782%   $201.7362   $201.74   $201.75   $201.70  
  Purchase #5 $36.95   5.726%   $39.0658   $39.07   $39.05   $39.10  
  Purchase #6 $150.58   11.195%   $167.4374   $167.44   $167.45   $167.40  
  Purchase #7 $157.65   10.617%   $174.3877   $174.39   $174.40   $174.40  
  7 purchase totals = $885.46       $970.5505   $970.56   $970.60   $970.50