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 $57.80   9.376%   $63.2193   $63.22   $63.20   $63.20  
  Purchase #2 $238.35   5.665%   $251.8525   $251.85   $251.85   $251.90  
  Purchase #3 $12.99   4.613%   $13.5892   $13.59   $13.60   $13.60  
  Purchase #4 $190.51   6.829%   $203.5199   $203.52   $203.50   $203.50  
  Purchase #5 $109.98   9.242%   $120.1444   $120.14   $120.15   $120.10  
  Purchase #6 $107.38   13.777%   $122.1737   $122.17   $122.15   $122.20  
  Purchase #7 $220.84   12.444%   $248.3213   $248.32   $248.30   $248.30  
  7 purchase totals = $937.85       $1,022.8203   $1,022.81   $1,022.75   $1,022.80