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 $96.53   11.740%   $107.8626   $107.86   $107.85   $107.90  
  Purchase #2 $57.52   8.126%   $62.1941   $62.19   $62.20   $62.20  
  Purchase #3 $176.46   4.679%   $184.7166   $184.72   $184.70   $184.70  
  Purchase #4 $165.36   3.831%   $171.6949   $171.69   $171.70   $171.70  
  Purchase #5 $62.70   4.696%   $65.6444   $65.64   $65.65   $65.60  
  Purchase #6 $205.92   10.189%   $226.9012   $226.90   $226.90   $226.90  
  Purchase #7 $219.52   4.844%   $230.1535   $230.15   $230.15   $230.20  
  7 purchase totals = $984.01       $1,049.1673   $1,049.15   $1,049.15   $1,049.20