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 $139.66   10.669%   $154.5603   $154.56   $154.55   $154.60  
  Purchase #2 $233.50   4.142%   $243.1716   $243.17   $243.15   $243.20  
  Purchase #3 $209.97   4.429%   $219.2696   $219.27   $219.25   $219.30  
  Purchase #4 $240.45   4.615%   $251.5468   $251.55   $251.55   $251.50  
  Purchase #5 $113.35   10.801%   $125.5929   $125.59   $125.60   $125.60  
  Purchase #6 $191.70   4.850%   $200.9975   $201.00   $201.00   $201.00  
  Purchase #7 $195.96   4.436%   $204.6528   $204.65   $204.65   $204.70  
  7 purchase totals = $1,324.59       $1,399.7915   $1,399.79   $1,399.75   $1,399.90