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 $118.74   6.701%   $126.6968   $126.70   $126.70   $126.70  
  Purchase #2 $230.75   7.127%   $247.1956   $247.20   $247.20   $247.20  
  Purchase #3 $222.62   10.118%   $245.1447   $245.14   $245.15   $245.10  
  Purchase #4 $110.49   6.826%   $118.032   $118.03   $118.05   $118.00  
  Purchase #5 $99.60   7.290%   $106.8608   $106.86   $106.85   $106.90  
  Purchase #6 $183.83   9.278%   $200.8857   $200.89   $200.90   $200.90  
  Purchase #7 $24.81   7.219%   $26.601   $26.60   $26.60   $26.60  
  7 purchase totals = $990.84       $1,071.4166   $1,071.42   $1,071.45   $1,071.40