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 $121.87   10.220%   $134.3251   $134.33   $134.35   $134.30  
  Purchase #2 $40.26   11.428%   $44.8609   $44.86   $44.85   $44.90  
  Purchase #3 $20.96   9.762%   $23.0061   $23.01   $23.00   $23.00  
  Purchase #4 $93.47   3.284%   $96.5396   $96.54   $96.55   $96.50  
  Purchase #5 $139.99   10.822%   $155.1397   $155.14   $155.15   $155.10  
  Purchase #6 $190.75   11.810%   $213.2776   $213.28   $213.30   $213.30  
  Purchase #7 $174.41   9.219%   $190.4889   $190.49   $190.50   $190.50  
  7 purchase totals = $781.71       $857.6379   $857.65   $857.70   $857.60