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 $220.81   12.243%   $247.8438   $247.84   $247.85   $247.80  
  Purchase #2 $203.32   5.823%   $215.1593   $215.16   $215.15   $215.20  
  Purchase #3 $112.72   13.415%   $127.8414   $127.84   $127.85   $127.80  
  Purchase #4 $68.95   6.724%   $73.5862   $73.59   $73.60   $73.60  
  Purchase #5 $156.28   8.574%   $169.6794   $169.68   $169.70   $169.70  
  Purchase #6 $133.78   13.721%   $152.136   $152.14   $152.15   $152.10  
  Purchase #7 $22.96   8.235%   $24.8508   $24.85   $24.85   $24.90  
  7 purchase totals = $918.82       $1,011.0969   $1,011.10   $1,011.15   $1,011.10