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 $142.52   4.155%   $148.4417   $148.44   $148.45   $148.40  
  Purchase #2 $71.84   8.615%   $78.029   $78.03   $78.05   $78.00  
  Purchase #3 $30.58   3.445%   $31.6335   $31.63   $31.65   $31.60  
  Purchase #4 $9.52   4.524%   $9.9507   $9.95   $9.95   $10.00  
  Purchase #5 $14.36   4.377%   $14.9885   $14.99   $15.00   $15.00  
  Purchase #6 $117.45   9.668%   $128.8051   $128.81   $128.80   $128.80  
  Purchase #7 $177.51   9.358%   $194.1214   $194.12   $194.10   $194.10  
  7 purchase totals = $563.78       $605.9699   $605.97   $606.00   $605.90