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 $219.47   7.494%   $235.9171   $235.92   $235.90   $235.90  
  Purchase #2 $118.25   5.378%   $124.6095   $124.61   $124.60   $124.60  
  Purchase #3 $145.52   13.243%   $164.7912   $164.79   $164.80   $164.80  
  Purchase #4 $230.33   9.621%   $252.49   $252.49   $252.50   $252.50  
  Purchase #5 $151.34   9.873%   $166.2818   $166.28   $166.30   $166.30  
  Purchase #6 $236.74   13.292%   $268.2075   $268.21   $268.20   $268.20  
  Purchase #7 $111.44   6.763%   $118.9767   $118.98   $119.00   $119.00  
  7 purchase totals = $1,213.09       $1,331.2738   $1,331.28   $1,331.30   $1,331.30