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 $66.54   11.231%   $74.0131   $74.01   $74.00   $74.00  
  Purchase #2 $205.72   6.453%   $218.9951   $219.00   $219.00   $219.00  
  Purchase #3 $146.28   6.551%   $155.8628   $155.86   $155.85   $155.90  
  Purchase #4 $233.97   9.130%   $255.3315   $255.33   $255.35   $255.30  
  Purchase #5 $92.58   4.202%   $96.4702   $96.47   $96.45   $96.50  
  Purchase #6 $44.52   8.233%   $48.1853   $48.19   $48.20   $48.20  
  Purchase #7 $210.29   7.706%   $226.4949   $226.49   $226.50   $226.50  
  7 purchase totals = $999.90       $1,075.3529   $1,075.35   $1,075.35   $1,075.40