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 $182.80   10.463%   $201.9264   $201.93   $201.95   $201.90  
  Purchase #2 $217.30   11.696%   $242.7154   $242.72   $242.70   $242.70  
  Purchase #3 $66.98   4.286%   $69.8508   $69.85   $69.85   $69.90  
  Purchase #4 $145.40   7.295%   $156.0069   $156.01   $156.00   $156.00  
  Purchase #5 $69.26   8.761%   $75.3279   $75.33   $75.35   $75.30  
  Purchase #6 $18.82   4.310%   $19.6311   $19.63   $19.65   $19.60  
  Purchase #7 $55.94   11.302%   $62.2623   $62.26   $62.25   $62.30  
  7 purchase totals = $756.50       $827.7208   $827.73   $827.75   $827.70