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 $229.28   12.156%   $257.1513   $257.15   $257.15   $257.20  
  Purchase #2 $226.88   3.421%   $234.6416   $234.64   $234.65   $234.60  
  Purchase #3 $32.76   11.166%   $36.418   $36.42   $36.40   $36.40  
  Purchase #4 $85.94   6.408%   $91.447   $91.45   $91.45   $91.40  
  Purchase #5 $187.67   10.626%   $207.6118   $207.61   $207.60   $207.60  
  Purchase #6 $155.47   10.827%   $172.3027   $172.30   $172.30   $172.30  
  Purchase #7 $23.68   8.418%   $25.6734   $25.67   $25.65   $25.70  
  7 purchase totals = $941.68       $1,025.2458   $1,025.24   $1,025.20   $1,025.20