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 $53.79   11.516%   $59.9845   $59.98   $60.00   $60.00  
  Purchase #2 $89.53   5.829%   $94.7487   $94.75   $94.75   $94.70  
  Purchase #3 $43.57   10.723%   $48.242   $48.24   $48.25   $48.20  
  Purchase #4 $10.51   9.607%   $11.5197   $11.52   $11.50   $11.50  
  Purchase #5 $228.55   9.859%   $251.0827   $251.08   $251.10   $251.10  
  Purchase #6 $231.73   3.358%   $239.5115   $239.51   $239.50   $239.50  
  Purchase #7 $36.52   5.839%   $38.6524   $38.65   $38.65   $38.70  
  7 purchase totals = $694.20       $743.7415   $743.73   $743.75   $743.70