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 $202.34   6.521%   $215.5346   $215.53   $215.55   $215.50  
  Purchase #2 $148.53   3.796%   $154.1682   $154.17   $154.15   $154.20  
  Purchase #3 $106.74   12.404%   $119.98   $119.98   $120.00   $120.00  
  Purchase #4 $117.40   4.676%   $122.8896   $122.89   $122.90   $122.90  
  Purchase #5 $250.72   5.310%   $264.0332   $264.03   $264.05   $264.00  
  Purchase #6 $104.88   12.411%   $117.8967   $117.90   $117.90   $117.90  
  Purchase #7 $91.74   12.379%   $103.0965   $103.10   $103.10   $103.10  
  7 purchase totals = $1,022.35       $1,097.5988   $1,097.60   $1,097.65   $1,097.60