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 $54.51   13.453%   $61.8432   $61.84   $61.85   $61.80  
  Purchase #2 $150.49   9.803%   $165.2425   $165.24   $165.25   $165.20  
  Purchase #3 $117.50   13.814%   $133.7315   $133.73   $133.75   $133.70  
  Purchase #4 $132.98   3.325%   $137.4016   $137.40   $137.40   $137.40  
  Purchase #5 $118.54   13.612%   $134.6757   $134.68   $134.70   $134.70  
  Purchase #6 $220.75   11.393%   $245.9   $245.90   $245.90   $245.90  
  Purchase #7 $16.68   7.565%   $17.9418   $17.94   $17.95   $17.90  
  7 purchase totals = $811.45       $896.7363   $896.73   $896.80   $896.60