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 $236.62   7.315%   $253.9288   $253.93   $253.95   $253.90  
  Purchase #2 $98.79   11.761%   $110.4087   $110.41   $110.40   $110.40  
  Purchase #3 $67.99   13.824%   $77.3889   $77.39   $77.40   $77.40  
  Purchase #4 $30.36   4.452%   $31.7116   $31.71   $31.70   $31.70  
  Purchase #5 $128.81   6.335%   $136.9701   $136.97   $136.95   $137.00  
  Purchase #6 $80.92   9.537%   $88.6373   $88.64   $88.65   $88.60  
  Purchase #7 $31.67   4.284%   $33.0267   $33.03   $33.05   $33.00  
  7 purchase totals = $675.16       $732.0721   $732.08   $732.10   $732.00