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 $93.45   3.351%   $96.5815   $96.58   $96.60   $96.60  
  Purchase #2 $32.95   3.240%   $34.0176   $34.02   $34.00   $34.00  
  Purchase #3 $227.62   4.656%   $238.218   $238.22   $238.20   $238.20  
  Purchase #4 $81.47   7.761%   $87.7929   $87.79   $87.80   $87.80  
  Purchase #5 $223.53   7.708%   $240.7597   $240.76   $240.75   $240.80  
  Purchase #6 $77.87   13.416%   $88.317   $88.32   $88.30   $88.30  
  Purchase #7 $161.76   4.380%   $168.8451   $168.85   $168.85   $168.80  
  7 purchase totals = $898.65       $954.5318   $954.54   $954.50   $954.50