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 $234.94   6.625%   $250.5048   $250.50   $250.50   $250.50  
  Purchase #2 $179.84   11.813%   $201.0845   $201.08   $201.10   $201.10  
  Purchase #3 $148.54   11.132%   $165.0755   $165.08   $165.10   $165.10  
  Purchase #4 $88.32   7.743%   $95.1586   $95.16   $95.15   $95.20  
  Purchase #5 $110.70   7.730%   $119.2571   $119.26   $119.25   $119.30  
  Purchase #6 $214.26   6.320%   $227.8012   $227.80   $227.80   $227.80  
  Purchase #7 $107.87   8.843%   $117.4089   $117.41   $117.40   $117.40  
  7 purchase totals = $1,084.47       $1,176.2906   $1,176.29   $1,176.30   $1,176.40