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 $82.43   13.652%   $93.6833   $93.68   $93.70   $93.70  
  Purchase #2 $155.90   3.274%   $161.0042   $161.00   $161.00   $161.00  
  Purchase #3 $27.63   6.777%   $29.5025   $29.50   $29.50   $29.50  
  Purchase #4 $181.50   6.415%   $193.1432   $193.14   $193.15   $193.10  
  Purchase #5 $192.78   9.470%   $211.0363   $211.04   $211.05   $211.00  
  Purchase #6 $204.82   11.824%   $229.0379   $229.04   $229.05   $229.00  
  Purchase #7 $73.97   5.374%   $77.9451   $77.95   $77.95   $77.90  
  7 purchase totals = $919.03       $995.3525   $995.35   $995.40   $995.20