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 $144.98   11.237%   $161.2714   $161.27   $161.25   $161.30  
  Purchase #2 $232.32   8.350%   $251.7187   $251.72   $251.70   $251.70  
  Purchase #3 $194.49   3.788%   $201.8573   $201.86   $201.85   $201.90  
  Purchase #4 $87.63   5.867%   $92.7713   $92.77   $92.75   $92.80  
  Purchase #5 $43.95   12.447%   $49.4205   $49.42   $49.40   $49.40  
  Purchase #6 $228.48   5.191%   $240.3404   $240.34   $240.35   $240.30  
  Purchase #7 $191.85   11.169%   $213.2777   $213.28   $213.30   $213.30  
  7 purchase totals = $1,123.70       $1,210.6573   $1,210.66   $1,210.60   $1,210.70