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 $208.70   12.833%   $235.4825   $235.48   $235.50   $235.50  
  Purchase #2 $140.62   13.169%   $159.1382   $159.14   $159.15   $159.10  
  Purchase #3 $103.99   6.346%   $110.5892   $110.59   $110.60   $110.60  
  Purchase #4 $133.51   4.751%   $139.8531   $139.85   $139.85   $139.90  
  Purchase #5 $71.49   6.226%   $75.941   $75.94   $75.95   $75.90  
  Purchase #6 $184.86   6.818%   $197.4638   $197.46   $197.45   $197.50  
  Purchase #7 $80.31   4.675%   $84.0645   $84.06   $84.05   $84.10  
  7 purchase totals = $923.48       $1,002.5323   $1,002.52   $1,002.55   $1,002.60