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 $169.66   3.788%   $176.0867   $176.09   $176.10   $176.10  
  Purchase #2 $62.67   11.222%   $69.7028   $69.70   $69.70   $69.70  
  Purchase #3 $27.36   7.701%   $29.467   $29.47   $29.45   $29.50  
  Purchase #4 $231.33   9.514%   $253.3387   $253.34   $253.35   $253.30  
  Purchase #5 $129.60   3.154%   $133.6876   $133.69   $133.70   $133.70  
  Purchase #6 $34.85   13.274%   $39.476   $39.48   $39.50   $39.50  
  Purchase #7 $58.67   11.721%   $65.5467   $65.55   $65.55   $65.50  
  7 purchase totals = $714.14       $767.3055   $767.32   $767.35   $767.30