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 $76.59   13.113%   $86.6332   $86.63   $86.65   $86.60  
  Purchase #2 $186.27   8.287%   $201.7062   $201.71   $201.70   $201.70  
  Purchase #3 $107.51   13.856%   $122.4066   $122.41   $122.40   $122.40  
  Purchase #4 $217.98   9.163%   $237.9535   $237.95   $237.95   $238.00  
  Purchase #5 $102.57   5.419%   $108.1283   $108.13   $108.15   $108.10  
  Purchase #6 $156.30   7.102%   $167.4004   $167.40   $167.40   $167.40  
  Purchase #7 $116.51   10.340%   $128.5571   $128.56   $128.55   $128.60  
  7 purchase totals = $963.73       $1,052.7853   $1,052.79   $1,052.80   $1,052.80