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 $194.59   5.393%   $205.0842   $205.08   $205.10   $205.10  
  Purchase #2 $15.26   7.364%   $16.3837   $16.38   $16.40   $16.40  
  Purchase #3 $229.70   10.866%   $254.6592   $254.66   $254.65   $254.70  
  Purchase #4 $99.27   5.674%   $104.9026   $104.90   $104.90   $104.90  
  Purchase #5 $126.30   10.853%   $140.0073   $140.01   $140.00   $140.00  
  Purchase #6 $212.74   4.349%   $221.9921   $221.99   $222.00   $222.00  
  Purchase #7 $72.51   11.676%   $80.9763   $80.98   $81.00   $81.00  
  7 purchase totals = $950.37       $1,024.0054   $1,024.00   $1,024.05   $1,024.10