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 $137.86   8.690%   $149.84   $149.84   $149.85   $149.80  
  Purchase #2 $190.73   12.295%   $214.1803   $214.18   $214.20   $214.20  
  Purchase #3 $193.55   13.627%   $219.9251   $219.93   $219.95   $219.90  
  Purchase #4 $28.73   3.494%   $29.7338   $29.73   $29.75   $29.70  
  Purchase #5 $84.30   7.205%   $90.3738   $90.37   $90.35   $90.40  
  Purchase #6 $71.73   10.539%   $79.2896   $79.29   $79.30   $79.30  
  Purchase #7 $109.55   6.174%   $116.3136   $116.31   $116.30   $116.30  
  7 purchase totals = $816.45       $899.6562   $899.65   $899.70   $899.60