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 $221.48   10.293%   $244.2769   $244.28   $244.30   $244.30  
  Purchase #2 $210.65   6.552%   $224.4518   $224.45   $224.45   $224.50  
  Purchase #3 $219.79   4.835%   $230.4168   $230.42   $230.40   $230.40  
  Purchase #4 $40.77   9.823%   $44.7748   $44.77   $44.75   $44.80  
  Purchase #5 $173.43   10.353%   $191.3852   $191.39   $191.40   $191.40  
  Purchase #6 $212.78   5.471%   $224.4212   $224.42   $224.40   $224.40  
  Purchase #7 $38.52   13.109%   $43.5696   $43.57   $43.55   $43.60  
  7 purchase totals = $1,117.42       $1,203.2963   $1,203.30   $1,203.25   $1,203.40