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 $205.65   7.591%   $221.2609   $221.26   $221.25   $221.30  
  Purchase #2 $121.68   6.687%   $129.8167   $129.82   $129.80   $129.80  
  Purchase #3 $10.74   4.772%   $11.2525   $11.25   $11.25   $11.30  
  Purchase #4 $56.87   6.534%   $60.5859   $60.59   $60.60   $60.60  
  Purchase #5 $36.95   13.626%   $41.9848   $41.98   $42.00   $42.00  
  Purchase #6 $195.59   3.598%   $202.6273   $202.63   $202.65   $202.60  
  Purchase #7 $80.40   6.458%   $85.5922   $85.59   $85.60   $85.60  
  7 purchase totals = $707.88       $753.1203   $753.12   $753.15   $753.20