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 $183.77   11.411%   $204.74   $204.74   $204.75   $204.70  
  Purchase #2 $122.33   11.635%   $136.5631   $136.56   $136.55   $136.60  
  Purchase #3 $39.81   8.491%   $43.1903   $43.19   $43.20   $43.20  
  Purchase #4 $172.77   6.669%   $184.292   $184.29   $184.30   $184.30  
  Purchase #5 $24.33   4.316%   $25.3801   $25.38   $25.40   $25.40  
  Purchase #6 $70.63   4.226%   $73.6148   $73.61   $73.60   $73.60  
  Purchase #7 $226.92   13.705%   $258.0194   $258.02   $258.00   $258.00  
  7 purchase totals = $840.56       $925.7997   $925.79   $925.80   $925.80