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 $159.51   13.752%   $181.4458   $181.45   $181.45   $181.40  
  Purchase #2 $22.80   12.497%   $25.6493   $25.65   $25.65   $25.60  
  Purchase #3 $237.75   13.165%   $269.0498   $269.05   $269.05   $269.00  
  Purchase #4 $211.38   5.574%   $223.1623   $223.16   $223.15   $223.20  
  Purchase #5 $190.69   5.652%   $201.4678   $201.47   $201.45   $201.50  
  Purchase #6 $170.68   10.798%   $189.11   $189.11   $189.10   $189.10  
  Purchase #7 $162.88   8.648%   $176.9659   $176.97   $176.95   $177.00  
  7 purchase totals = $1,155.69       $1,266.8509   $1,266.86   $1,266.80   $1,266.80