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 $208.56   11.587%   $232.7258   $232.73   $232.75   $232.70  
  Purchase #2 $8.36   11.174%   $9.2941   $9.29   $9.30   $9.30  
  Purchase #3 $51.85   13.476%   $58.8373   $58.84   $58.85   $58.80  
  Purchase #4 $10.66   8.685%   $11.5858   $11.59   $11.60   $11.60  
  Purchase #5 $191.26   8.527%   $207.5687   $207.57   $207.55   $207.60  
  Purchase #6 $152.45   8.444%   $165.3229   $165.32   $165.30   $165.30  
  Purchase #7 $226.66   5.196%   $238.4373   $238.44   $238.45   $238.40  
  7 purchase totals = $849.80       $923.7719   $923.78   $923.80   $923.70