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 $162.95   9.650%   $178.6747   $178.67   $178.65   $178.70  
  Purchase #2 $26.28   8.287%   $28.4578   $28.46   $28.45   $28.50  
  Purchase #3 $59.62   11.286%   $66.3487   $66.35   $66.35   $66.30  
  Purchase #4 $204.77   12.812%   $231.0051   $231.01   $231.00   $231.00  
  Purchase #5 $151.89   9.543%   $166.3849   $166.38   $166.40   $166.40  
  Purchase #6 $121.60   3.374%   $125.7028   $125.70   $125.70   $125.70  
  Purchase #7 $226.63   5.592%   $239.3031   $239.30   $239.30   $239.30  
  7 purchase totals = $953.74       $1,035.8771   $1,035.87   $1,035.85   $1,035.90