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 $96.83   7.766%   $104.3498   $104.35   $104.35   $104.30  
  Purchase #2 $193.96   5.658%   $204.9343   $204.93   $204.95   $204.90  
  Purchase #3 $141.80   9.707%   $155.5645   $155.56   $155.55   $155.60  
  Purchase #4 $245.61   6.769%   $262.2353   $262.24   $262.25   $262.20  
  Purchase #5 $183.82   13.210%   $208.1026   $208.10   $208.10   $208.10  
  Purchase #6 $234.25   12.322%   $263.1143   $263.11   $263.10   $263.10  
  Purchase #7 $79.90   6.246%   $84.8906   $84.89   $84.90   $84.90  
  7 purchase totals = $1,176.17       $1,283.1914   $1,283.18   $1,283.20   $1,283.10