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 $58.97   5.521%   $62.2257   $62.23   $62.25   $62.20  
  Purchase #2 $12.56   6.387%   $13.3622   $13.36   $13.35   $13.40  
  Purchase #3 $214.66   6.282%   $228.1449   $228.14   $228.15   $228.10  
  Purchase #4 $77.81   13.528%   $88.3361   $88.34   $88.35   $88.30  
  Purchase #5 $203.29   13.781%   $231.3054   $231.31   $231.30   $231.30  
  Purchase #6 $128.83   4.129%   $134.1494   $134.15   $134.15   $134.10  
  Purchase #7 $232.47   3.783%   $241.2643   $241.26   $241.25   $241.30  
  7 purchase totals = $928.59       $998.7880   $998.79   $998.80   $998.70