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 $46.34   11.821%   $51.8179   $51.82   $51.80   $51.80  
  Purchase #2 $122.41   4.809%   $128.2967   $128.30   $128.30   $128.30  
  Purchase #3 $24.56   7.834%   $26.484   $26.48   $26.50   $26.50  
  Purchase #4 $187.32   9.716%   $205.52   $205.52   $205.50   $205.50  
  Purchase #5 $36.56   5.174%   $38.4516   $38.45   $38.45   $38.50  
  Purchase #6 $228.50   7.114%   $244.7555   $244.76   $244.75   $244.80  
  Purchase #7 $225.48   11.358%   $251.09   $251.09   $251.10   $251.10  
  7 purchase totals = $871.17       $946.4157   $946.42   $946.40   $946.50