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 $244.90   8.524%   $265.7753   $265.78   $265.80   $265.80  
  Purchase #2 $34.43   7.222%   $36.9165   $36.92   $36.90   $36.90  
  Purchase #3 $49.89   7.586%   $53.6747   $53.67   $53.65   $53.70  
  Purchase #4 $60.33   3.677%   $62.5483   $62.55   $62.55   $62.50  
  Purchase #5 $56.75   13.192%   $64.2365   $64.24   $64.25   $64.20  
  Purchase #6 $224.48   8.859%   $244.3667   $244.37   $244.35   $244.40  
  Purchase #7 $250.52   5.280%   $263.7475   $263.75   $263.75   $263.70  
  7 purchase totals = $921.30       $991.2655   $991.28   $991.25   $991.20