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 $206.42   8.409%   $223.7779   $223.78   $223.80   $223.80  
  Purchase #2 $134.71   8.859%   $146.644   $146.64   $146.65   $146.60  
  Purchase #3 $110.72   12.702%   $124.7837   $124.78   $124.80   $124.80  
  Purchase #4 $193.48   5.540%   $204.1988   $204.20   $204.20   $204.20  
  Purchase #5 $150.65   8.839%   $163.966   $163.97   $163.95   $164.00  
  Purchase #6 $22.76   4.674%   $23.8238   $23.82   $23.80   $23.80  
  Purchase #7 $123.73   9.541%   $135.5351   $135.54   $135.55   $135.50  
  7 purchase totals = $942.47       $1,022.7293   $1,022.73   $1,022.75   $1,022.70