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 $99.91   9.412%   $109.3135   $109.31   $109.30   $109.30  
  Purchase #2 $221.80   9.432%   $242.7202   $242.72   $242.70   $242.70  
  Purchase #3 $21.71   6.800%   $23.1863   $23.19   $23.20   $23.20  
  Purchase #4 $213.94   6.708%   $228.2911   $228.29   $228.30   $228.30  
  Purchase #5 $222.52   12.667%   $250.7066   $250.71   $250.70   $250.70  
  Purchase #6 $86.80   3.774%   $90.0758   $90.08   $90.10   $90.10  
  Purchase #7 $219.99   6.789%   $234.9251   $234.93   $234.95   $234.90  
  7 purchase totals = $1,086.67       $1,179.2186   $1,179.23   $1,179.25   $1,179.20