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 $19.82   12.432%   $22.284   $22.28   $22.30   $22.30  
  Purchase #2 $53.63   5.666%   $56.6687   $56.67   $56.65   $56.70  
  Purchase #3 $215.94   6.853%   $230.7384   $230.74   $230.75   $230.70  
  Purchase #4 $201.40   4.554%   $210.5718   $210.57   $210.55   $210.60  
  Purchase #5 $83.40   10.585%   $92.2279   $92.23   $92.25   $92.20  
  Purchase #6 $186.26   13.749%   $211.8689   $211.87   $211.85   $211.90  
  Purchase #7 $47.30   8.543%   $51.3408   $51.34   $51.35   $51.30  
  7 purchase totals = $807.75       $875.7005   $875.70   $875.70   $875.70