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 $203.81   10.545%   $225.3018   $225.30   $225.30   $225.30  
  Purchase #2 $88.62   13.537%   $100.6165   $100.62   $100.60   $100.60  
  Purchase #3 $177.69   3.862%   $184.5524   $184.55   $184.55   $184.60  
  Purchase #4 $165.57   7.217%   $177.5192   $177.52   $177.50   $177.50  
  Purchase #5 $210.27   7.342%   $225.708   $225.71   $225.70   $225.70  
  Purchase #6 $42.93   11.773%   $47.9841   $47.98   $48.00   $48.00  
  Purchase #7 $58.80   6.523%   $62.6355   $62.64   $62.65   $62.60  
  7 purchase totals = $947.69       $1,024.3175   $1,024.32   $1,024.30   $1,024.30