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 $136.99   12.312%   $153.8562   $153.86   $153.85   $153.90  
  Purchase #2 $245.79   9.102%   $268.1618   $268.16   $268.15   $268.20  
  Purchase #3 $147.81   11.445%   $164.7269   $164.73   $164.75   $164.70  
  Purchase #4 $126.34   9.313%   $138.106   $138.11   $138.10   $138.10  
  Purchase #5 $198.49   9.535%   $217.416   $217.42   $217.40   $217.40  
  Purchase #6 $187.42   7.210%   $200.933   $200.93   $200.95   $200.90  
  Purchase #7 $69.95   4.804%   $73.3104   $73.31   $73.30   $73.30  
  7 purchase totals = $1,112.79       $1,216.5103   $1,216.52   $1,216.50   $1,216.50