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 $234.40   7.732%   $252.5238   $252.52   $252.50   $252.50  
  Purchase #2 $191.81   7.488%   $206.1727   $206.17   $206.15   $206.20  
  Purchase #3 $54.75   9.293%   $59.8379   $59.84   $59.85   $59.80  
  Purchase #4 $207.30   13.352%   $234.9787   $234.98   $235.00   $235.00  
  Purchase #5 $14.82   6.407%   $15.7695   $15.77   $15.75   $15.80  
  Purchase #6 $139.63   8.133%   $150.9861   $150.99   $151.00   $151.00  
  Purchase #7 $181.46   8.823%   $197.4702   $197.47   $197.45   $197.50  
  7 purchase totals = $1,024.17       $1,117.7389   $1,117.74   $1,117.70   $1,117.80