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 $203.96   11.123%   $226.6465   $226.65   $226.65   $226.60  
  Purchase #2 $206.87   6.398%   $220.1055   $220.11   $220.10   $220.10  
  Purchase #3 $20.96   12.740%   $23.6303   $23.63   $23.65   $23.60  
  Purchase #4 $197.78   7.214%   $212.0478   $212.05   $212.05   $212.00  
  Purchase #5 $157.32   3.621%   $163.0166   $163.02   $163.00   $163.00  
  Purchase #6 $14.51   12.732%   $16.3574   $16.36   $16.35   $16.40  
  Purchase #7 $158.48   4.130%   $165.0252   $165.03   $165.05   $165.00  
  7 purchase totals = $959.88       $1,026.8293   $1,026.85   $1,026.85   $1,026.70