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 $121.46   3.731%   $125.9917   $125.99   $126.00   $126.00  
  Purchase #2 $217.56   6.135%   $230.9073   $230.91   $230.90   $230.90  
  Purchase #3 $113.82   7.531%   $122.3918   $122.39   $122.40   $122.40  
  Purchase #4 $48.45   11.195%   $53.874   $53.87   $53.85   $53.90  
  Purchase #5 $10.52   10.785%   $11.6546   $11.65   $11.65   $11.70  
  Purchase #6 $72.54   11.461%   $80.8538   $80.85   $80.85   $80.90  
  Purchase #7 $128.52   4.789%   $134.6748   $134.67   $134.65   $134.70  
  7 purchase totals = $712.87       $760.3480   $760.33   $760.30   $760.50