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 $161.93   13.231%   $183.355   $183.36   $183.35   $183.40  
  Purchase #2 $83.96   13.211%   $95.052   $95.05   $95.05   $95.10  
  Purchase #3 $135.68   10.165%   $149.4719   $149.47   $149.45   $149.50  
  Purchase #4 $24.39   12.365%   $27.4058   $27.41   $27.40   $27.40  
  Purchase #5 $171.26   13.776%   $194.8528   $194.85   $194.85   $194.90  
  Purchase #6 $201.97   7.864%   $217.8529   $217.85   $217.85   $217.90  
  Purchase #7 $141.89   11.292%   $157.9122   $157.91   $157.90   $157.90  
  7 purchase totals = $921.08       $1,025.9026   $1,025.90   $1,025.85   $1,026.10