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 $108.41   10.416%   $119.702   $119.70   $119.70   $119.70  
  Purchase #2 $102.66   10.395%   $113.3315   $113.33   $113.35   $113.30  
  Purchase #3 $97.44   6.447%   $103.722   $103.72   $103.70   $103.70  
  Purchase #4 $69.50   12.821%   $78.4106   $78.41   $78.40   $78.40  
  Purchase #5 $83.51   5.837%   $88.3845   $88.38   $88.40   $88.40  
  Purchase #6 $154.90   9.819%   $170.1096   $170.11   $170.10   $170.10  
  Purchase #7 $80.35   5.751%   $84.9709   $84.97   $84.95   $85.00  
  7 purchase totals = $696.77       $758.6311   $758.62   $758.60   $758.60