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 $108.33   3.236%   $111.8356   $111.84   $111.85   $111.80  
  Purchase #2 $84.82   9.245%   $92.6616   $92.66   $92.65   $92.70  
  Purchase #3 $168.63   5.140%   $177.2976   $177.30   $177.30   $177.30  
  Purchase #4 $78.66   4.690%   $82.3492   $82.35   $82.35   $82.30  
  Purchase #5 $175.29   10.799%   $194.2196   $194.22   $194.20   $194.20  
  Purchase #6 $180.74   13.569%   $205.2646   $205.26   $205.25   $205.30  
  Purchase #7 $165.32   11.706%   $184.6724   $184.67   $184.65   $184.70  
  7 purchase totals = $961.79       $1,048.3006   $1,048.30   $1,048.25   $1,048.30