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 $68.37   3.671%   $70.8799   $70.88   $70.90   $70.90  
  Purchase #2 $96.30   9.716%   $105.6565   $105.66   $105.65   $105.70  
  Purchase #3 $196.29   6.170%   $208.4011   $208.40   $208.40   $208.40  
  Purchase #4 $205.35   11.302%   $228.5587   $228.56   $228.55   $228.60  
  Purchase #5 $41.71   7.677%   $44.9121   $44.91   $44.90   $44.90  
  Purchase #6 $176.74   11.780%   $197.56   $197.56   $197.55   $197.60  
  Purchase #7 $235.75   9.718%   $258.6602   $258.66   $258.65   $258.70  
  7 purchase totals = $1,020.51       $1,114.6285   $1,114.63   $1,114.60   $1,114.80