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 $61.51   12.475%   $69.1834   $69.18   $69.20   $69.20  
  Purchase #2 $240.55   12.695%   $271.0878   $271.09   $271.10   $271.10  
  Purchase #3 $58.27   13.520%   $66.1481   $66.15   $66.15   $66.10  
  Purchase #4 $181.26   3.352%   $187.3358   $187.34   $187.35   $187.30  
  Purchase #5 $167.45   13.275%   $189.679   $189.68   $189.70   $189.70  
  Purchase #6 $165.58   7.771%   $178.4472   $178.45   $178.45   $178.40  
  Purchase #7 $220.38   12.389%   $247.6829   $247.68   $247.70   $247.70  
  7 purchase totals = $1,095.00       $1,209.5642   $1,209.57   $1,209.65   $1,209.50