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 $47.46   12.217%   $53.2582   $53.26   $53.25   $53.30  
  Purchase #2 $63.51   4.780%   $66.5458   $66.55   $66.55   $66.50  
  Purchase #3 $195.75   9.364%   $214.08   $214.08   $214.10   $214.10  
  Purchase #4 $183.49   11.381%   $204.373   $204.37   $204.35   $204.40  
  Purchase #5 $122.50   7.472%   $131.6532   $131.65   $131.65   $131.70  
  Purchase #6 $133.84   13.266%   $151.5952   $151.60   $151.60   $151.60  
  Purchase #7 $185.61   10.715%   $205.4981   $205.50   $205.50   $205.50  
  7 purchase totals = $932.16       $1,027.0035   $1,027.01   $1,027.00   $1,027.10