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 $67.42   4.540%   $70.4809   $70.48   $70.50   $70.50  
  Purchase #2 $176.51   11.818%   $197.37   $197.37   $197.35   $197.40  
  Purchase #3 $41.55   7.433%   $44.6384   $44.64   $44.65   $44.60  
  Purchase #4 $226.70   13.653%   $257.6514   $257.65   $257.65   $257.70  
  Purchase #5 $89.57   5.594%   $94.5805   $94.58   $94.60   $94.60  
  Purchase #6 $46.77   9.154%   $51.0513   $51.05   $51.05   $51.10  
  Purchase #7 $38.84   4.454%   $40.5699   $40.57   $40.55   $40.60  
  7 purchase totals = $687.36       $756.3424   $756.34   $756.35   $756.50