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 $9.92   4.462%   $10.3626   $10.36   $10.35   $10.40  
  Purchase #2 $11.72   9.725%   $12.8598   $12.86   $12.85   $12.90  
  Purchase #3 $54.74   6.107%   $58.083   $58.08   $58.10   $58.10  
  Purchase #4 $197.37   13.335%   $223.6893   $223.69   $223.70   $223.70  
  Purchase #5 $184.47   10.619%   $204.0589   $204.06   $204.05   $204.10  
  Purchase #6 $101.39   3.637%   $105.0776   $105.08   $105.10   $105.10  
  Purchase #7 $73.99   8.393%   $80.2   $80.20   $80.20   $80.20  
  7 purchase totals = $633.60       $694.3312   $694.33   $694.35   $694.50