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 $210.64   11.539%   $234.9457   $234.95   $234.95   $234.90  
  Purchase #2 $139.92   7.357%   $150.2139   $150.21   $150.20   $150.20  
  Purchase #3 $189.46   8.359%   $205.297   $205.30   $205.30   $205.30  
  Purchase #4 $55.88   10.511%   $61.7535   $61.75   $61.75   $61.80  
  Purchase #5 $73.73   10.838%   $81.7209   $81.72   $81.70   $81.70  
  Purchase #6 $188.84   3.523%   $195.4928   $195.49   $195.50   $195.50  
  Purchase #7 $112.46   13.385%   $127.5128   $127.51   $127.50   $127.50  
  7 purchase totals = $970.93       $1,056.9366   $1,056.93   $1,056.90   $1,056.90