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 $226.99   12.166%   $254.6056   $254.61   $254.60   $254.60  
  Purchase #2 $152.45   4.625%   $159.5008   $159.50   $159.50   $159.50  
  Purchase #3 $244.30   7.517%   $262.664   $262.66   $262.65   $262.70  
  Purchase #4 $149.64   11.122%   $166.283   $166.28   $166.30   $166.30  
  Purchase #5 $65.59   6.632%   $69.9399   $69.94   $69.95   $69.90  
  Purchase #6 $144.87   7.402%   $155.5933   $155.59   $155.60   $155.60  
  Purchase #7 $168.52   11.338%   $187.6268   $187.63   $187.65   $187.60  
  7 purchase totals = $1,152.36       $1,256.2134   $1,256.21   $1,256.25   $1,256.20