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 $74.82   6.286%   $79.5232   $79.52   $79.50   $79.50  
  Purchase #2 $111.77   4.362%   $116.6454   $116.65   $116.65   $116.60  
  Purchase #3 $113.50   4.384%   $118.4758   $118.48   $118.50   $118.50  
  Purchase #4 $200.64   8.839%   $218.3746   $218.37   $218.35   $218.40  
  Purchase #5 $232.85   12.601%   $262.1914   $262.19   $262.20   $262.20  
  Purchase #6 $82.87   12.391%   $93.1384   $93.14   $93.15   $93.10  
  Purchase #7 $160.97   6.735%   $171.8113   $171.81   $171.80   $171.80  
  7 purchase totals = $977.42       $1,060.1601   $1,060.16   $1,060.15   $1,060.10