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 $53.52   9.482%   $58.5948   $58.59   $58.60   $58.60  
  Purchase #2 $204.63   11.593%   $228.3528   $228.35   $228.35   $228.40  
  Purchase #3 $152.67   6.348%   $162.3615   $162.36   $162.35   $162.40  
  Purchase #4 $41.64   8.381%   $45.1298   $45.13   $45.15   $45.10  
  Purchase #5 $83.75   8.504%   $90.8721   $90.87   $90.85   $90.90  
  Purchase #6 $187.97   10.544%   $207.7896   $207.79   $207.80   $207.80  
  Purchase #7 $122.48   7.773%   $132.0004   $132.00   $132.00   $132.00  
  7 purchase totals = $846.66       $925.1010   $925.09   $925.10   $925.20