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 $238.74   3.852%   $247.9363   $247.94   $247.95   $247.90  
  Purchase #2 $19.69   7.284%   $21.1242   $21.12   $21.10   $21.10  
  Purchase #3 $210.68   7.773%   $227.0562   $227.06   $227.05   $227.10  
  Purchase #4 $240.69   7.749%   $259.3411   $259.34   $259.35   $259.30  
  Purchase #5 $184.51   11.494%   $205.7176   $205.72   $205.70   $205.70  
  Purchase #6 $221.51   6.174%   $235.186   $235.19   $235.20   $235.20  
  Purchase #7 $53.52   5.240%   $56.3244   $56.32   $56.30   $56.30  
  7 purchase totals = $1,169.34       $1,252.6858   $1,252.69   $1,252.65   $1,252.60