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 $49.58   4.855%   $51.9871   $51.99   $52.00   $52.00  
  Purchase #2 $234.28   10.386%   $258.6123   $258.61   $258.60   $258.60  
  Purchase #3 $208.44   5.396%   $219.6874   $219.69   $219.70   $219.70  
  Purchase #4 $229.94   5.137%   $241.752   $241.75   $241.75   $241.80  
  Purchase #5 $26.58   12.630%   $29.9371   $29.94   $29.95   $29.90  
  Purchase #6 $40.99   10.430%   $45.2653   $45.27   $45.25   $45.30  
  Purchase #7 $204.34   4.137%   $212.7935   $212.79   $212.80   $212.80  
  7 purchase totals = $994.15       $1,060.0347   $1,060.04   $1,060.05   $1,060.10