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 $116.85   12.661%   $131.6444   $131.64   $131.65   $131.60  
  Purchase #2 $181.57   11.230%   $201.9603   $201.96   $201.95   $202.00  
  Purchase #3 $122.38   9.414%   $133.9009   $133.90   $133.90   $133.90  
  Purchase #4 $44.25   5.164%   $46.5351   $46.54   $46.55   $46.50  
  Purchase #5 $67.82   10.415%   $74.8835   $74.88   $74.90   $74.90  
  Purchase #6 $113.83   5.376%   $119.9495   $119.95   $119.95   $119.90  
  Purchase #7 $229.41   6.722%   $244.8309   $244.83   $244.85   $244.80  
  7 purchase totals = $876.11       $953.7046   $953.70   $953.75   $953.60