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 $117.98   13.803%   $134.2648   $134.26   $134.25   $134.30  
  Purchase #2 $202.59   11.833%   $226.5625   $226.56   $226.55   $226.60  
  Purchase #3 $184.79   8.179%   $199.904   $199.90   $199.90   $199.90  
  Purchase #4 $211.86   4.165%   $220.684   $220.68   $220.70   $220.70  
  Purchase #5 $233.30   7.214%   $250.1303   $250.13   $250.15   $250.10  
  Purchase #6 $232.84   4.627%   $243.6135   $243.61   $243.60   $243.60  
  Purchase #7 $187.70   3.268%   $193.834   $193.83   $193.85   $193.80  
  7 purchase totals = $1,371.06       $1,468.9931   $1,468.97   $1,469.00   $1,469.00