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 $39.45   9.650%   $43.2569   $43.26   $43.25   $43.30  
  Purchase #2 $249.49   13.428%   $282.9915   $282.99   $283.00   $283.00  
  Purchase #3 $181.59   6.444%   $193.2917   $193.29   $193.30   $193.30  
  Purchase #4 $161.58   6.464%   $172.0245   $172.02   $172.00   $172.00  
  Purchase #5 $59.65   4.332%   $62.234   $62.23   $62.25   $62.20  
  Purchase #6 $186.36   13.534%   $211.582   $211.58   $211.60   $211.60  
  Purchase #7 $60.29   7.678%   $64.9191   $64.92   $64.90   $64.90  
  7 purchase totals = $938.41       $1,030.2997   $1,030.29   $1,030.30   $1,030.30