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 $85.38   9.443%   $93.4424   $93.44   $93.45   $93.40  
  Purchase #2 $105.37   10.623%   $116.5635   $116.56   $116.55   $116.60  
  Purchase #3 $26.90   5.182%   $28.294   $28.29   $28.30   $28.30  
  Purchase #4 $220.30   4.742%   $230.7466   $230.75   $230.75   $230.70  
  Purchase #5 $161.43   5.806%   $170.8026   $170.80   $170.80   $170.80  
  Purchase #6 $169.51   5.345%   $178.5703   $178.57   $178.55   $178.60  
  Purchase #7 $8.55   6.314%   $9.0898   $9.09   $9.10   $9.10  
  7 purchase totals = $777.44       $827.5092   $827.50   $827.50   $827.50