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 $162.62   10.811%   $180.2008   $180.20   $180.20   $180.20  
  Purchase #2 $93.27   3.285%   $96.3339   $96.33   $96.35   $96.30  
  Purchase #3 $207.98   10.577%   $229.978   $229.98   $230.00   $230.00  
  Purchase #4 $244.36   12.587%   $275.1176   $275.12   $275.10   $275.10  
  Purchase #5 $161.55   9.518%   $176.9263   $176.93   $176.95   $176.90  
  Purchase #6 $31.85   8.594%   $34.5872   $34.59   $34.60   $34.60  
  Purchase #7 $145.40   8.737%   $158.1036   $158.10   $158.10   $158.10  
  7 purchase totals = $1,047.03       $1,151.2474   $1,151.25   $1,151.30   $1,151.20