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 $39.27   5.849%   $41.5669   $41.57   $41.55   $41.60  
  Purchase #2 $200.76   6.438%   $213.6849   $213.68   $213.70   $213.70  
  Purchase #3 $226.34   3.869%   $235.0971   $235.10   $235.10   $235.10  
  Purchase #4 $88.27   3.437%   $91.3038   $91.30   $91.30   $91.30  
  Purchase #5 $11.50   9.654%   $12.6102   $12.61   $12.60   $12.60  
  Purchase #6 $231.60   5.667%   $244.7248   $244.72   $244.70   $244.70  
  Purchase #7 $112.84   9.642%   $123.72   $123.72   $123.70   $123.70  
  7 purchase totals = $910.58       $962.7077   $962.70   $962.65   $962.70