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 $41.34   4.557%   $43.2239   $43.22   $43.20   $43.20  
  Purchase #2 $151.82   9.564%   $166.3401   $166.34   $166.35   $166.30  
  Purchase #3 $215.29   8.833%   $234.3066   $234.31   $234.30   $234.30  
  Purchase #4 $235.31   13.599%   $267.3098   $267.31   $267.30   $267.30  
  Purchase #5 $67.69   9.679%   $74.2417   $74.24   $74.25   $74.20  
  Purchase #6 $131.62   10.326%   $145.2111   $145.21   $145.20   $145.20  
  Purchase #7 $64.34   5.841%   $68.0981   $68.10   $68.10   $68.10  
  7 purchase totals = $907.41       $998.7313   $998.73   $998.70   $998.60