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 $214.66   9.131%   $234.2606   $234.26   $234.25   $234.30  
  Purchase #2 $110.99   8.338%   $120.2443   $120.24   $120.25   $120.20  
  Purchase #3 $45.68   13.363%   $51.7842   $51.78   $51.80   $51.80  
  Purchase #4 $145.46   13.618%   $165.2687   $165.27   $165.25   $165.30  
  Purchase #5 $201.43   7.516%   $216.5695   $216.57   $216.55   $216.60  
  Purchase #6 $240.58   10.245%   $265.2274   $265.23   $265.25   $265.20  
  Purchase #7 $48.96   7.769%   $52.7637   $52.76   $52.75   $52.80  
  7 purchase totals = $1,007.76       $1,106.1184   $1,106.11   $1,106.10   $1,106.20