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 $238.29   12.569%   $268.2407   $268.24   $268.25   $268.20  
  Purchase #2 $125.35   4.282%   $130.7175   $130.72   $130.70   $130.70  
  Purchase #3 $245.41   7.677%   $264.2501   $264.25   $264.25   $264.30  
  Purchase #4 $173.83   11.182%   $193.2677   $193.27   $193.25   $193.30  
  Purchase #5 $138.53   4.310%   $144.5006   $144.50   $144.50   $144.50  
  Purchase #6 $106.81   3.215%   $110.2439   $110.24   $110.25   $110.20  
  Purchase #7 $35.26   3.386%   $36.4539   $36.45   $36.45   $36.50  
  7 purchase totals = $1,063.48       $1,147.6744   $1,147.67   $1,147.65   $1,147.70