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 $207.82   6.618%   $221.5735   $221.57   $221.55   $221.60  
  Purchase #2 $164.65   3.641%   $170.6449   $170.64   $170.65   $170.60  
  Purchase #3 $43.59   10.183%   $48.0288   $48.03   $48.05   $48.00  
  Purchase #4 $124.41   8.130%   $134.5245   $134.52   $134.50   $134.50  
  Purchase #5 $95.76   6.473%   $101.9585   $101.96   $101.95   $102.00  
  Purchase #6 $143.43   6.862%   $153.2722   $153.27   $153.25   $153.30  
  Purchase #7 $206.93   11.317%   $230.3483   $230.35   $230.35   $230.30  
  7 purchase totals = $986.59       $1,060.3507   $1,060.34   $1,060.30   $1,060.30