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 $200.57   12.539%   $225.7195   $225.72   $225.70   $225.70  
  Purchase #2 $58.92   3.596%   $61.0388   $61.04   $61.05   $61.00  
  Purchase #3 $104.84   12.189%   $117.6189   $117.62   $117.60   $117.60  
  Purchase #4 $178.85   7.871%   $192.9273   $192.93   $192.95   $192.90  
  Purchase #5 $106.31   4.108%   $110.6772   $110.68   $110.70   $110.70  
  Purchase #6 $167.83   5.222%   $176.5941   $176.59   $176.60   $176.60  
  Purchase #7 $9.70   10.123%   $10.6819   $10.68   $10.70   $10.70  
  7 purchase totals = $827.02       $895.2577   $895.26   $895.30   $895.20