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 $52.86   11.668%   $59.0277   $59.03   $59.05   $59.00  
  Purchase #2 $200.97   4.182%   $209.3746   $209.37   $209.35   $209.40  
  Purchase #3 $176.96   5.349%   $186.4256   $186.43   $186.45   $186.40  
  Purchase #4 $123.47   9.144%   $134.7601   $134.76   $134.75   $134.80  
  Purchase #5 $195.47   3.756%   $202.8119   $202.81   $202.80   $202.80  
  Purchase #6 $197.96   7.179%   $212.1715   $212.17   $212.15   $212.20  
  Purchase #7 $156.51   12.542%   $176.1395   $176.14   $176.15   $176.10  
  7 purchase totals = $1,104.20       $1,180.7109   $1,180.71   $1,180.70   $1,180.70