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 $40.47   12.757%   $45.6328   $45.63   $45.65   $45.60  
  Purchase #2 $232.55   8.519%   $252.3609   $252.36   $252.35   $252.40  
  Purchase #3 $11.93   13.690%   $13.5632   $13.56   $13.55   $13.60  
  Purchase #4 $77.34   10.583%   $85.5249   $85.52   $85.50   $85.50  
  Purchase #5 $116.29   8.161%   $125.7804   $125.78   $125.80   $125.80  
  Purchase #6 $245.54   6.767%   $262.1557   $262.16   $262.15   $262.20  
  Purchase #7 $246.46   9.548%   $269.992   $269.99   $270.00   $270.00  
  7 purchase totals = $970.58       $1,055.0099   $1,055.00   $1,055.00   $1,055.10