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 $180.41   13.361%   $204.5146   $204.51   $204.50   $204.50  
  Purchase #2 $111.82   9.430%   $122.3646   $122.36   $122.35   $122.40  
  Purchase #3 $12.99   12.404%   $14.6013   $14.60   $14.60   $14.60  
  Purchase #4 $157.85   8.257%   $170.8837   $170.88   $170.90   $170.90  
  Purchase #5 $180.86   7.224%   $193.9253   $193.93   $193.95   $193.90  
  Purchase #6 $181.56   10.477%   $200.582   $200.58   $200.60   $200.60  
  Purchase #7 $152.99   12.396%   $171.9546   $171.95   $171.95   $172.00  
  7 purchase totals = $978.48       $1,078.8261   $1,078.81   $1,078.85   $1,078.90