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 $106.53   11.517%   $118.7991   $118.80   $118.80   $118.80  
  Purchase #2 $56.74   12.169%   $63.6447   $63.64   $63.65   $63.60  
  Purchase #3 $204.41   3.689%   $211.9507   $211.95   $211.95   $212.00  
  Purchase #4 $168.69   4.686%   $176.5948   $176.59   $176.60   $176.60  
  Purchase #5 $137.51   13.444%   $155.9968   $156.00   $156.00   $156.00  
  Purchase #6 $87.89   3.419%   $90.895   $90.90   $90.90   $90.90  
  Purchase #7 $185.47   8.687%   $201.5818   $201.58   $201.60   $201.60  
  7 purchase totals = $947.24       $1,019.4629   $1,019.46   $1,019.50   $1,019.50