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 $36.48   12.546%   $41.0568   $41.06   $41.05   $41.10  
  Purchase #2 $231.39   8.498%   $251.0535   $251.05   $251.05   $251.10  
  Purchase #3 $140.77   10.503%   $155.5551   $155.56   $155.55   $155.60  
  Purchase #4 $217.71   12.290%   $244.4666   $244.47   $244.45   $244.50  
  Purchase #5 $99.79   3.724%   $103.5062   $103.51   $103.50   $103.50  
  Purchase #6 $21.95   8.410%   $23.796   $23.80   $23.80   $23.80  
  Purchase #7 $231.54   4.427%   $241.7903   $241.79   $241.80   $241.80  
  7 purchase totals = $979.63       $1,061.2245   $1,061.24   $1,061.20   $1,061.40