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 $58.52   12.146%   $65.6278   $65.63   $65.65   $65.60  
  Purchase #2 $165.55   5.171%   $174.1106   $174.11   $174.10   $174.10  
  Purchase #3 $176.43   7.553%   $189.7558   $189.76   $189.75   $189.80  
  Purchase #4 $229.94   4.675%   $240.6897   $240.69   $240.70   $240.70  
  Purchase #5 $103.34   10.330%   $114.015   $114.02   $114.00   $114.00  
  Purchase #6 $83.81   4.811%   $87.8421   $87.84   $87.85   $87.80  
  Purchase #7 $198.41   6.186%   $210.6836   $210.68   $210.70   $210.70  
  7 purchase totals = $1,016.00       $1,082.7246   $1,082.73   $1,082.75   $1,082.70