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 $64.98   7.273%   $69.706   $69.71   $69.70   $69.70  
  Purchase #2 $234.29   6.565%   $249.6711   $249.67   $249.65   $249.70  
  Purchase #3 $62.28   7.205%   $66.7673   $66.77   $66.75   $66.80  
  Purchase #4 $228.34   7.350%   $245.123   $245.12   $245.10   $245.10  
  Purchase #5 $64.44   6.110%   $68.3773   $68.38   $68.40   $68.40  
  Purchase #6 $224.94   3.544%   $232.9119   $232.91   $232.90   $232.90  
  Purchase #7 $202.97   10.446%   $224.1722   $224.17   $224.15   $224.20  
  7 purchase totals = $1,082.24       $1,156.7288   $1,156.73   $1,156.65   $1,156.80