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 $191.59   6.842%   $204.6986   $204.70   $204.70   $204.70  
  Purchase #2 $171.55   8.398%   $185.9568   $185.96   $185.95   $186.00  
  Purchase #3 $37.85   7.525%   $40.6982   $40.70   $40.70   $40.70  
  Purchase #4 $89.80   4.641%   $93.9676   $93.97   $93.95   $94.00  
  Purchase #5 $217.49   7.759%   $234.365   $234.37   $234.35   $234.40  
  Purchase #6 $238.89   4.213%   $248.9544   $248.95   $248.95   $249.00  
  Purchase #7 $223.67   9.645%   $245.243   $245.24   $245.25   $245.20  
  7 purchase totals = $1,170.84       $1,253.8836   $1,253.89   $1,253.85   $1,254.00