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 $203.29   11.476%   $226.6196   $226.62   $226.60   $226.60  
  Purchase #2 $115.69   7.566%   $124.4431   $124.44   $124.45   $124.40  
  Purchase #3 $155.88   3.285%   $161.0007   $161.00   $161.00   $161.00  
  Purchase #4 $230.30   10.107%   $253.5764   $253.58   $253.60   $253.60  
  Purchase #5 $128.63   13.391%   $145.8548   $145.85   $145.85   $145.90  
  Purchase #6 $62.94   11.427%   $70.1322   $70.13   $70.15   $70.10  
  Purchase #7 $39.25   4.121%   $40.8675   $40.87   $40.85   $40.90  
  7 purchase totals = $935.98       $1,022.4943   $1,022.49   $1,022.50   $1,022.50