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 $168.82   13.290%   $191.2562   $191.26   $191.25   $191.30  
  Purchase #2 $149.52   3.377%   $154.5693   $154.57   $154.55   $154.60  
  Purchase #3 $124.32   3.866%   $129.1262   $129.13   $129.15   $129.10  
  Purchase #4 $59.65   11.623%   $66.5831   $66.58   $66.60   $66.60  
  Purchase #5 $215.98   13.716%   $245.6038   $245.60   $245.60   $245.60  
  Purchase #6 $187.69   8.543%   $203.7244   $203.72   $203.70   $203.70  
  Purchase #7 $70.41   6.162%   $74.7487   $74.75   $74.75   $74.70  
  7 purchase totals = $976.39       $1,065.6117   $1,065.61   $1,065.60   $1,065.60