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 $161.65   9.514%   $177.0294   $177.03   $177.05   $177.00  
  Purchase #2 $81.47   12.870%   $91.9552   $91.96   $91.95   $92.00  
  Purchase #3 $158.96   8.294%   $172.1441   $172.14   $172.15   $172.10  
  Purchase #4 $59.27   7.245%   $63.5641   $63.56   $63.55   $63.60  
  Purchase #5 $226.75   7.421%   $243.5771   $243.58   $243.60   $243.60  
  Purchase #6 $150.77   5.813%   $159.5343   $159.53   $159.55   $159.50  
  Purchase #7 $96.37   3.112%   $99.369   $99.37   $99.35   $99.40  
  7 purchase totals = $935.24       $1,007.1732   $1,007.17   $1,007.20   $1,007.20