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 $61.33   12.376%   $68.9202   $68.92   $68.90   $68.90  
  Purchase #2 $116.73   10.554%   $129.0497   $129.05   $129.05   $129.00  
  Purchase #3 $54.46   11.829%   $60.9021   $60.90   $60.90   $60.90  
  Purchase #4 $65.59   12.841%   $74.0124   $74.01   $74.00   $74.00  
  Purchase #5 $60.80   13.456%   $68.9812   $68.98   $69.00   $69.00  
  Purchase #6 $61.31   10.652%   $67.8407   $67.84   $67.85   $67.80  
  Purchase #7 $15.96   9.612%   $17.4941   $17.49   $17.50   $17.50  
  7 purchase totals = $436.18       $487.2004   $487.19   $487.20   $487.10