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 $192.47   8.139%   $208.1351   $208.14   $208.15   $208.10  
  Purchase #2 $222.90   8.119%   $240.9973   $241.00   $241.00   $241.00  
  Purchase #3 $247.31   7.113%   $264.9012   $264.90   $264.90   $264.90  
  Purchase #4 $48.38   9.578%   $53.0138   $53.01   $53.00   $53.00  
  Purchase #5 $60.97   8.590%   $66.2073   $66.21   $66.20   $66.20  
  Purchase #6 $17.27   3.464%   $17.8682   $17.87   $17.85   $17.90  
  Purchase #7 $165.46   13.442%   $187.7011   $187.70   $187.70   $187.70  
  7 purchase totals = $954.76       $1,038.8240   $1,038.83   $1,038.80   $1,038.80