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 $94.91   3.813%   $98.5289   $98.53   $98.55   $98.50  
  Purchase #2 $212.62   7.325%   $228.1944   $228.19   $228.20   $228.20  
  Purchase #3 $117.32   8.672%   $127.494   $127.49   $127.50   $127.50  
  Purchase #4 $62.29   8.479%   $67.5716   $67.57   $67.55   $67.60  
  Purchase #5 $54.27   13.458%   $61.5737   $61.57   $61.55   $61.60  
  Purchase #6 $169.73   9.786%   $186.3398   $186.34   $186.35   $186.30  
  Purchase #7 $60.60   4.309%   $63.2113   $63.21   $63.20   $63.20  
  7 purchase totals = $771.74       $832.9137   $832.90   $832.90   $832.90