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 $126.57   10.616%   $140.0067   $140.01   $140.00   $140.00  
  Purchase #2 $11.72   5.297%   $12.3408   $12.34   $12.35   $12.30  
  Purchase #3 $85.66   11.408%   $95.4321   $95.43   $95.45   $95.40  
  Purchase #4 $79.74   3.805%   $82.7741   $82.77   $82.75   $82.80  
  Purchase #5 $14.55   11.177%   $16.1763   $16.18   $16.20   $16.20  
  Purchase #6 $218.25   6.425%   $232.2726   $232.27   $232.25   $232.30  
  Purchase #7 $64.77   9.271%   $70.7748   $70.77   $70.75   $70.80  
  7 purchase totals = $601.26       $649.7774   $649.77   $649.75   $649.80