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 $242.41   13.682%   $275.5765   $275.58   $275.60   $275.60  
  Purchase #2 $159.51   5.740%   $168.6659   $168.67   $168.65   $168.70  
  Purchase #3 $182.93   8.774%   $198.9803   $198.98   $199.00   $199.00  
  Purchase #4 $232.60   3.812%   $241.4667   $241.47   $241.45   $241.50  
  Purchase #5 $126.98   4.729%   $132.9849   $132.98   $133.00   $133.00  
  Purchase #6 $137.99   11.443%   $153.7802   $153.78   $153.80   $153.80  
  Purchase #7 $193.33   7.597%   $208.0173   $208.02   $208.00   $208.00  
  7 purchase totals = $1,275.75       $1,379.4718   $1,379.48   $1,379.50   $1,379.60