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 $55.60   11.569%   $62.0324   $62.03   $62.05   $62.00  
  Purchase #2 $163.86   7.815%   $176.6657   $176.67   $176.65   $176.70  
  Purchase #3 $71.32   7.824%   $76.9001   $76.90   $76.90   $76.90  
  Purchase #4 $49.97   7.356%   $53.6458   $53.65   $53.65   $53.60  
  Purchase #5 $175.45   7.574%   $188.7386   $188.74   $188.75   $188.70  
  Purchase #6 $96.70   13.821%   $110.0649   $110.06   $110.05   $110.10  
  Purchase #7 $184.52   3.474%   $190.9302   $190.93   $190.95   $190.90  
  7 purchase totals = $797.42       $858.9777   $858.98   $859.00   $858.90