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 $227.34   13.753%   $258.6061   $258.61   $258.60   $258.60  
  Purchase #2 $6.87   7.749%   $7.4024   $7.40   $7.40   $7.40  
  Purchase #3 $55.62   7.853%   $59.9878   $59.99   $60.00   $60.00  
  Purchase #4 $111.99   13.371%   $126.9642   $126.96   $126.95   $127.00  
  Purchase #5 $54.57   3.621%   $56.546   $56.55   $56.55   $56.50  
  Purchase #6 $237.52   4.317%   $247.7737   $247.77   $247.75   $247.80  
  Purchase #7 $215.95   6.690%   $230.3971   $230.40   $230.40   $230.40  
  7 purchase totals = $909.86       $987.6773   $987.68   $987.65   $987.70