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 $194.43   5.803%   $205.7128   $205.71   $205.70   $205.70  
  Purchase #2 $199.71   3.517%   $206.7338   $206.73   $206.75   $206.70  
  Purchase #3 $90.52   8.618%   $98.321   $98.32   $98.30   $98.30  
  Purchase #4 $60.50   6.145%   $64.2177   $64.22   $64.20   $64.20  
  Purchase #5 $180.60   12.874%   $203.8504   $203.85   $203.85   $203.90  
  Purchase #6 $212.31   12.672%   $239.2139   $239.21   $239.20   $239.20  
  Purchase #7 $15.71   6.553%   $16.7395   $16.74   $16.75   $16.70  
  7 purchase totals = $953.78       $1,034.7891   $1,034.78   $1,034.75   $1,034.70