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 $92.44   12.517%   $104.0107   $104.01   $104.00   $104.00  
  Purchase #2 $88.62   9.337%   $96.8944   $96.89   $96.90   $96.90  
  Purchase #3 $95.91   5.371%   $101.0613   $101.06   $101.05   $101.10  
  Purchase #4 $145.56   5.785%   $153.9806   $153.98   $154.00   $154.00  
  Purchase #5 $226.26   3.384%   $233.9166   $233.92   $233.90   $233.90  
  Purchase #6 $71.57   3.367%   $73.9798   $73.98   $74.00   $74.00  
  Purchase #7 $179.44   9.819%   $197.0592   $197.06   $197.05   $197.10  
  7 purchase totals = $899.80       $960.9026   $960.90   $960.90   $961.00