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 $34.71   8.852%   $37.7825   $37.78   $37.80   $37.80  
  Purchase #2 $208.82   13.336%   $236.6682   $236.67   $236.65   $236.70  
  Purchase #3 $54.35   4.641%   $56.8724   $56.87   $56.85   $56.90  
  Purchase #4 $110.25   6.464%   $117.3766   $117.38   $117.40   $117.40  
  Purchase #5 $27.37   7.716%   $29.4819   $29.48   $29.50   $29.50  
  Purchase #6 $141.69   6.784%   $151.3022   $151.30   $151.30   $151.30  
  Purchase #7 $69.50   8.716%   $75.5576   $75.56   $75.55   $75.60  
  7 purchase totals = $646.69       $705.0414   $705.04   $705.05   $705.20