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 $232.59   9.313%   $254.2511   $254.25   $254.25   $254.30  
  Purchase #2 $110.33   7.495%   $118.5992   $118.60   $118.60   $118.60  
  Purchase #3 $166.84   8.603%   $181.1932   $181.19   $181.20   $181.20  
  Purchase #4 $69.61   3.270%   $71.8862   $71.89   $71.90   $71.90  
  Purchase #5 $25.38   7.817%   $27.364   $27.36   $27.35   $27.40  
  Purchase #6 $132.28   6.122%   $140.3782   $140.38   $140.40   $140.40  
  Purchase #7 $106.63   10.806%   $118.1524   $118.15   $118.15   $118.20  
  7 purchase totals = $843.66       $911.8243   $911.82   $911.85   $912.00