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 $54.74   4.190%   $57.0336   $57.03   $57.05   $57.00  
  Purchase #2 $183.83   10.596%   $203.3086   $203.31   $203.30   $203.30  
  Purchase #3 $185.61   5.310%   $195.4659   $195.47   $195.45   $195.50  
  Purchase #4 $226.61   11.282%   $252.1761   $252.18   $252.20   $252.20  
  Purchase #5 $234.75   7.682%   $252.7835   $252.78   $252.80   $252.80  
  Purchase #6 $15.96   3.130%   $16.4595   $16.46   $16.45   $16.50  
  Purchase #7 $45.58   8.332%   $49.3777   $49.38   $49.40   $49.40  
  7 purchase totals = $947.08       $1,026.6049   $1,026.61   $1,026.65   $1,026.70